diff --git a/requirements.txt b/requirements.txt
index 97dc7cd..2522ad0 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,2 +1,4 @@
 fastapi
 uvicorn
+pytest
+httpx
diff --git a/src/app.py b/src/app.py
index 4ebb1d9..a913c19 100644
--- a/src/app.py
+++ b/src/app.py
@@ -38,6 +38,42 @@
         "schedule": "Mondays, Wednesdays, Fridays, 2:00 PM - 3:00 PM",
         "max_participants": 30,
         "participants": ["john@mergington.edu", "olivia@mergington.edu"]
+    },
+    "Basketball": {
+        "description": "Team sport focusing on basketball skills and competitive play",
+        "schedule": "Mondays and Wednesdays, 4:00 PM - 5:30 PM",
+        "max_participants": 15,
+        "participants": ["alex@mergington.edu"]
+    },
+    "Tennis Club": {
+        "description": "Learn tennis techniques and participate in matches",
+        "schedule": "Saturdays, 10:00 AM - 11:30 AM",
+        "max_participants": 10,
+        "participants": ["james@mergington.edu"]
+    },
+    "Drama Club": {
+        "description": "Perform in theatrical productions and develop acting skills",
+        "schedule": "Wednesdays and Thursdays, 4:00 PM - 5:30 PM",
+        "max_participants": 25,
+        "participants": ["isabella@mergington.edu", "lucas@mergington.edu"]
+    },
+    "Art Studio": {
+        "description": "Create visual art including painting, drawing, and sculpture",
+        "schedule": "Tuesdays and Fridays, 3:30 PM - 5:00 PM",
+        "max_participants": 18,
+        "participants": ["sophie@mergington.edu"]
+    },
+    "Debate Team": {
+        "description": "Develop public speaking and argumentation skills",
+        "schedule": "Mondays and Thursdays, 3:30 PM - 4:45 PM",
+        "max_participants": 16,
+        "participants": ["noah@mergington.edu", "ava@mergington.edu"]
+    },
+    "Science Club": {
+        "description": "Explore scientific concepts through experiments and projects",
+        "schedule": "Wednesdays, 3:30 PM - 5:00 PM",
+        "max_participants": 20,
+        "participants": ["ethan@mergington.edu"]
     }
 }
 
@@ -62,6 +98,29 @@ def signup_for_activity(activity_name: str, email: str):
     # Get the specific activity
     activity = activities[activity_name]
 
+    # Validate student is not already signed up
+    if email in activity["participants"]:
+        raise HTTPException(status_code=400, detail="Student already signed up for this activity")
+
     # Add student
     activity["participants"].append(email)
     return {"message": f"Signed up {email} for {activity_name}"}
+
+
+@app.delete("/activities/{activity_name}/participants/{email}")
+def remove_participant(activity_name: str, email: str):
+    """Remove a participant from an activity"""
+    # Validate activity exists
+    if activity_name not in activities:
+        raise HTTPException(status_code=404, detail="Activity not found")
+
+    # Get the specific activity
+    activity = activities[activity_name]
+
+    # Validate student is signed up
+    if email not in activity["participants"]:
+        raise HTTPException(status_code=400, detail="Student is not signed up for this activity")
+
+    # Remove student
+    activity["participants"].remove(email)
+    return {"message": f"Removed {email} from {activity_name}"}
diff --git a/src/static/app.js b/src/static/app.js
index dcc1e38..9b5f7d7 100644
--- a/src/static/app.js
+++ b/src/static/app.js
@@ -25,6 +25,17 @@ document.addEventListener("DOMContentLoaded", () => {
           <p>${details.description}</p>
           <p><strong>Schedule:</strong> ${details.schedule}</p>
           <p><strong>Availability:</strong> ${spotsLeft} spots left</p>
+          <div class="participants">
+            <h5>Participants (${details.participants.length})</h5>
+            <ul>
+              ${details.participants.map(participant => `
+                <li>
+                  <span>${participant}</span>
+                  <button class="delete-btn" data-activity="${name}" data-email="${participant}" title="Remove participant">🗑️</button>
+                </li>
+              `).join('')}
+            </ul>
+          </div>
         `;
 
         activitiesList.appendChild(activityCard);
@@ -62,6 +73,8 @@ document.addEventListener("DOMContentLoaded", () => {
         messageDiv.textContent = result.message;
         messageDiv.className = "success";
         signupForm.reset();
+        // Reload activities to show the new participant
+        fetchActivities();
       } else {
         messageDiv.textContent = result.detail || "An error occurred";
         messageDiv.className = "error";
@@ -81,6 +94,48 @@ document.addEventListener("DOMContentLoaded", () => {
     }
   });
 
+  // Handle delete button clicks
+  activitiesList.addEventListener("click", async (event) => {
+    if (event.target.classList.contains("delete-btn")) {
+      const button = event.target;
+      const activity = button.getAttribute("data-activity");
+      const email = button.getAttribute("data-email");
+
+      try {
+        const response = await fetch(
+          `/activities/${encodeURIComponent(activity)}/participants/${encodeURIComponent(email)}`,
+          {
+            method: "DELETE",
+          }
+        );
+
+        const result = await response.json();
+
+        if (response.ok) {
+          messageDiv.textContent = result.message;
+          messageDiv.className = "success";
+          // Reload activities
+          fetchActivities();
+        } else {
+          messageDiv.textContent = result.detail || "Failed to remove participant";
+          messageDiv.className = "error";
+        }
+
+        messageDiv.classList.remove("hidden");
+
+        // Hide message after 5 seconds
+        setTimeout(() => {
+          messageDiv.classList.add("hidden");
+        }, 5000);
+      } catch (error) {
+        messageDiv.textContent = "Failed to remove participant. Please try again.";
+        messageDiv.className = "error";
+        messageDiv.classList.remove("hidden");
+        console.error("Error removing participant:", error);
+      }
+    }
+  });
+
   // Initialize app
   fetchActivities();
 });
diff --git a/src/static/styles.css b/src/static/styles.css
index a533b32..f66d90f 100644
--- a/src/static/styles.css
+++ b/src/static/styles.css
@@ -74,6 +74,52 @@ section h3 {
   margin-bottom: 8px;
 }
 
+.activity-card .participants {
+  margin-top: 15px;
+  padding-top: 15px;
+  border-top: 1px solid #e0e0e0;
+}
+
+.activity-card .participants h5 {
+  margin-bottom: 10px;
+  color: #1a237e;
+  font-size: 14px;
+  font-weight: bold;
+}
+
+.activity-card .participants ul {
+  margin-left: 0;
+  list-style-type: none;
+}
+
+.activity-card .participants li {
+  margin-bottom: 6px;
+  color: #555;
+  font-size: 14px;
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+}
+
+.activity-card .participants li span {
+  flex: 1;
+}
+
+.delete-btn {
+  background-color: transparent;
+  border: none;
+  font-size: 18px;
+  cursor: pointer;
+  padding: 4px 8px;
+  margin-left: 10px;
+  transition: transform 0.2s;
+}
+
+.delete-btn:hover {
+  background-color: transparent;
+  transform: scale(1.2);
+}
+
 .form-group {
   margin-bottom: 15px;
 }
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/tests/test_app.py b/tests/test_app.py
new file mode 100644
index 0000000..e580fa3
--- /dev/null
+++ b/tests/test_app.py
@@ -0,0 +1,241 @@
+"""
+Tests for the Mergington High School Activities API
+"""
+
+import pytest
+from fastapi.testclient import TestClient
+import sys
+from pathlib import Path
+
+# Add src directory to path so we can import app
+sys.path.insert(0, str(Path(__file__).parent.parent / "src"))
+
+from app import app
+
+client = TestClient(app)
+
+
+@pytest.fixture
+def reset_activities():
+    """Reset activities to initial state before each test"""
+    from app import activities
+    
+    # Store original state
+    original_activities = {
+        "Chess Club": {
+            "description": "Learn strategies and compete in chess tournaments",
+            "schedule": "Fridays, 3:30 PM - 5:00 PM",
+            "max_participants": 12,
+            "participants": ["michael@mergington.edu", "daniel@mergington.edu"]
+        },
+        "Programming Class": {
+            "description": "Learn programming fundamentals and build software projects",
+            "schedule": "Tuesdays and Thursdays, 3:30 PM - 4:30 PM",
+            "max_participants": 20,
+            "participants": ["emma@mergington.edu", "sophia@mergington.edu"]
+        },
+        "Gym Class": {
+            "description": "Physical education and sports activities",
+            "schedule": "Mondays, Wednesdays, Fridays, 2:00 PM - 3:00 PM",
+            "max_participants": 30,
+            "participants": ["john@mergington.edu", "olivia@mergington.edu"]
+        },
+        "Basketball": {
+            "description": "Team sport focusing on basketball skills and competitive play",
+            "schedule": "Mondays and Wednesdays, 4:00 PM - 5:30 PM",
+            "max_participants": 15,
+            "participants": ["alex@mergington.edu"]
+        },
+        "Tennis Club": {
+            "description": "Learn tennis techniques and participate in matches",
+            "schedule": "Saturdays, 10:00 AM - 11:30 AM",
+            "max_participants": 10,
+            "participants": ["james@mergington.edu"]
+        },
+        "Drama Club": {
+            "description": "Perform in theatrical productions and develop acting skills",
+            "schedule": "Wednesdays and Thursdays, 4:00 PM - 5:30 PM",
+            "max_participants": 25,
+            "participants": ["isabella@mergington.edu", "lucas@mergington.edu"]
+        },
+        "Art Studio": {
+            "description": "Create visual art including painting, drawing, and sculpture",
+            "schedule": "Tuesdays and Fridays, 3:30 PM - 5:00 PM",
+            "max_participants": 18,
+            "participants": ["sophie@mergington.edu"]
+        },
+        "Debate Team": {
+            "description": "Develop public speaking and argumentation skills",
+            "schedule": "Mondays and Thursdays, 3:30 PM - 4:45 PM",
+            "max_participants": 16,
+            "participants": ["noah@mergington.edu", "ava@mergington.edu"]
+        },
+        "Science Club": {
+            "description": "Explore scientific concepts through experiments and projects",
+            "schedule": "Wednesdays, 3:30 PM - 5:00 PM",
+            "max_participants": 20,
+            "participants": ["ethan@mergington.edu"]
+        }
+    }
+    
+    # Clear and reset
+    activities.clear()
+    activities.update(original_activities)
+    
+    yield
+    
+    # Restore after test
+    activities.clear()
+    activities.update(original_activities)
+
+
+class TestGetActivities:
+    """Tests for GET /activities endpoint"""
+    
+    def test_get_activities_returns_all_activities(self, reset_activities):
+        """Test that GET /activities returns all activities"""
+        response = client.get("/activities")
+        assert response.status_code == 200
+        
+        data = response.json()
+        assert "Chess Club" in data
+        assert "Programming Class" in data
+        assert len(data) == 9
+    
+    def test_activities_have_required_fields(self, reset_activities):
+        """Test that each activity has required fields"""
+        response = client.get("/activities")
+        data = response.json()
+        
+        for activity_name, activity_data in data.items():
+            assert "description" in activity_data
+            assert "schedule" in activity_data
+            assert "max_participants" in activity_data
+            assert "participants" in activity_data
+    
+    def test_activities_have_participants(self, reset_activities):
+        """Test that activities contain participants"""
+        response = client.get("/activities")
+        data = response.json()
+        
+        assert len(data["Chess Club"]["participants"]) == 2
+        assert "michael@mergington.edu" in data["Chess Club"]["participants"]
+
+
+class TestSignupForActivity:
+    """Tests for POST /activities/{activity_name}/signup endpoint"""
+    
+    def test_successful_signup(self, reset_activities):
+        """Test successfully signing up for an activity"""
+        response = client.post(
+            "/activities/Chess%20Club/signup?email=newstudent@mergington.edu",
+            headers={"Content-Type": "application/json"}
+        )
+        assert response.status_code == 200
+        data = response.json()
+        assert "Signed up" in data["message"]
+        assert "newstudent@mergington.edu" in data["message"]
+    
+    def test_signup_adds_participant(self, reset_activities):
+        """Test that signup actually adds the participant"""
+        client.post(
+            "/activities/Basketball/signup?email=newplayer@mergington.edu",
+            headers={"Content-Type": "application/json"}
+        )
+        
+        response = client.get("/activities")
+        data = response.json()
+        assert "newplayer@mergington.edu" in data["Basketball"]["participants"]
+    
+    def test_signup_for_nonexistent_activity(self, reset_activities):
+        """Test signing up for a nonexistent activity"""
+        response = client.post(
+            "/activities/Nonexistent%20Club/signup?email=student@mergington.edu",
+            headers={"Content-Type": "application/json"}
+        )
+        assert response.status_code == 404
+        data = response.json()
+        assert "Activity not found" in data["detail"]
+    
+    def test_signup_duplicate_email(self, reset_activities):
+        """Test signing up with an email already registered"""
+        response = client.post(
+            "/activities/Chess%20Club/signup?email=michael@mergington.edu",
+            headers={"Content-Type": "application/json"}
+        )
+        assert response.status_code == 400
+        data = response.json()
+        assert "already signed up" in data["detail"]
+    
+    def test_multiple_signups(self, reset_activities):
+        """Test multiple students signing up"""
+        client.post(
+            "/activities/Tennis%20Club/signup?email=student1@mergington.edu",
+            headers={"Content-Type": "application/json"}
+        )
+        client.post(
+            "/activities/Tennis%20Club/signup?email=student2@mergington.edu",
+            headers={"Content-Type": "application/json"}
+        )
+        
+        response = client.get("/activities")
+        data = response.json()
+        assert len(data["Tennis Club"]["participants"]) == 3
+        assert "student1@mergington.edu" in data["Tennis Club"]["participants"]
+        assert "student2@mergington.edu" in data["Tennis Club"]["participants"]
+
+
+class TestRemoveParticipant:
+    """Tests for DELETE /activities/{activity_name}/participants/{email} endpoint"""
+    
+    def test_successful_removal(self, reset_activities):
+        """Test successfully removing a participant"""
+        response = client.delete(
+            "/activities/Chess%20Club/participants/michael@mergington.edu"
+        )
+        assert response.status_code == 200
+        data = response.json()
+        assert "Removed" in data["message"]
+        assert "michael@mergington.edu" in data["message"]
+    
+    def test_removal_updates_participants_list(self, reset_activities):
+        """Test that removal actually removes the participant"""
+        client.delete(
+            "/activities/Drama%20Club/participants/isabella@mergington.edu"
+        )
+        
+        response = client.get("/activities")
+        data = response.json()
+        assert "isabella@mergington.edu" not in data["Drama Club"]["participants"]
+        assert len(data["Drama Club"]["participants"]) == 1
+    
+    def test_remove_from_nonexistent_activity(self, reset_activities):
+        """Test removing from a nonexistent activity"""
+        response = client.delete(
+            "/activities/Nonexistent%20Club/participants/student@mergington.edu"
+        )
+        assert response.status_code == 404
+        data = response.json()
+        assert "Activity not found" in data["detail"]
+    
+    def test_remove_nonexistent_participant(self, reset_activities):
+        """Test removing a participant who's not signed up"""
+        response = client.delete(
+            "/activities/Chess%20Club/participants/notregistered@mergington.edu"
+        )
+        assert response.status_code == 400
+        data = response.json()
+        assert "not signed up" in data["detail"]
+    
+    def test_remove_multiple_participants(self, reset_activities):
+        """Test removing multiple participants"""
+        client.delete(
+            "/activities/Debate%20Team/participants/noah@mergington.edu"
+        )
+        client.delete(
+            "/activities/Debate%20Team/participants/ava@mergington.edu"
+        )
+        
+        response = client.get("/activities")
+        data = response.json()
+        assert len(data["Debate Team"]["participants"]) == 0