diff --git a/campaign/src/lib.rs b/campaign/src/lib.rs
index ea92d8d..9a9df45 100644
--- a/campaign/src/lib.rs
+++ b/campaign/src/lib.rs
@@ -3,14 +3,124 @@
 pub mod storage;
 pub mod types;
 
-use soroban_sdk::{contract, contractimpl, Env};
+use soroban_sdk::{contract, contractimpl, Env, Vec};
+use types::{AssetInfo, CampaignData, CampaignStatus, Error, MilestoneData};
+use storage::{get_campaign, set_campaign, set_milestone};
 
 #[contract]
 pub struct CampaignContract;
 
 #[contractimpl]
 impl CampaignContract {
+    /// Initialize a new campaign with strict validation on all inputs.
+    ///
+    /// # Panics
+    /// - `Error::InvalidGoalAmount` if goal_amount <= 0
+    /// - `Error::InvalidEndTime` if end_time <= current ledger timestamp
+    /// - `Error::InvalidAssets` if accepted_assets is empty
+    /// - `Error::InvalidMilestones` if milestones are not sorted ascending by target_amount
+    /// - `Error::MilestoneMismatch` if last milestone.target_amount != goal_amount
+    pub fn initialize(
+        env: Env,
+        creator: soroban_sdk::Address,
+        goal_amount: i128,
+        end_time: u64,
+        accepted_assets: Vec<AssetInfo>,
+        milestones: Vec<MilestoneData>,
+    ) -> Result<(), Error> {
+        // Validation 1: goal_amount > 0
+        if goal_amount <= 0 {
+            panic_with_error(&env, Error::InvalidGoalAmount);
+        }
+
+        // Validation 2: end_time > current ledger timestamp
+        let current_timestamp = env.ledger().timestamp();
+        if end_time <= current_timestamp {
+            panic_with_error(&env, Error::InvalidEndTime);
+        }
+
+        // Validation 3: accepted_assets non-empty
+        if accepted_assets.is_empty() {
+            panic_with_error(&env, Error::InvalidAssets);
+        }
+
+        // Validation 4 & 5: milestones sorted ascending and last == goal_amount
+        if !milestones.is_empty() {
+            validate_milestones(&env, &milestones, goal_amount)?;
+        }
+
+        // All validations passed, store campaign data
+        let campaign = CampaignData {
+            creator,
+            goal_amount,
+            raised_amount: 0,
+            end_time,
+            status: CampaignStatus::Active,
+            accepted_assets,
+            milestone_count: milestones.len() as u32,
+        };
+
+        set_campaign(&env, &campaign);
+
+        // Store each milestone
+        for (index, milestone) in milestones.iter().enumerate() {
+            set_milestone(&env, index as u32, milestone);
+        }
+
+        Ok(())
+    }
+
     pub fn hello(env: Env) -> soroban_sdk::Symbol {
         soroban_sdk::Symbol::new(&env, "campaign")
     }
 }
+
+/// Helper function to validate milestone conditions
+fn validate_milestones(
+    env: &Env,
+    milestones: &Vec<MilestoneData>,
+    goal_amount: i128,
+) -> Result<(), Error> {
+    // Check if milestones are sorted ascending by target_amount
+    for i in 1..milestones.len() {
+        let prev = &milestones.get(i - 1).unwrap();
+        let current = &milestones.get(i).unwrap();
+
+        if prev.target_amount >= current.target_amount {
+            panic_with_error(env, Error::InvalidMilestones);
+        }
+    }
+
+    // Check if last milestone.target_amount == goal_amount
+    if let Some(last_milestone) = milestones.last() {
+        if last_milestone.target_amount != goal_amount {
+            panic_with_error(env, Error::MilestoneMismatch);
+        }
+    } else {
+        panic_with_error(env, Error::InvalidMilestones);
+    }
+
+    Ok(())
+}
+
+/// Helper function to panic with a descriptive error message
+fn panic_with_error(env: &Env, error: Error) -> ! {
+    match error {
+        Error::InvalidGoalAmount => {
+            env.panic_with_error(soroban_sdk::Symbol::new(env, "InvalidGoalAmount"))
+        }
+        Error::InvalidEndTime => {
+            env.panic_with_error(soroban_sdk::Symbol::new(env, "InvalidEndTime"))
+        }
+        Error::InvalidAssets => {
+            env.panic_with_error(soroban_sdk::Symbol::new(env, "InvalidAssets"))
+        }
+        Error::InvalidMilestones => {
+            env.panic_with_error(soroban_sdk::Symbol::new(env, "InvalidMilestones"))
+        }
+        Error::MilestoneMismatch => {
+            env.panic_with_error(soroban_sdk::Symbol::new(env, "MilestoneMismatch"))
+        }
+    }
+}
+
diff --git a/campaign/src/types.rs b/campaign/src/types.rs
index 6e4f0de..5cb3c94 100644
--- a/campaign/src/types.rs
+++ b/campaign/src/types.rs
@@ -1,5 +1,18 @@
 use soroban_sdk::{contracttype, Address, BytesN, Vec};
 
+// ── Error enum ──────────────────────────────────────────────────────────────
+
+/// Initialization validation errors
+#[contracttype]
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum Error {
+    InvalidGoalAmount,    // goal_amount must be > 0
+    InvalidEndTime,       // end_time must be > current ledger timestamp
+    InvalidAssets,        // accepted_assets must be non-empty
+    InvalidMilestones,    // milestones must be sorted ascending and last must equal goal
+    MilestoneMismatch,    // last milestone.target_amount != goal_amount
+}
+
 // ── Supporting enums ─────────────────────────────────────────────────────────
 
 /// Issue #167 – campaign lifecycle status