diff --git a/src/index.ts b/src/index.ts
index dd56ebb..c9ad378 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -26,7 +26,25 @@ export interface IArrayEnumerator<T> extends IEnumerator<T> {
 }
 
 export interface IEnumerable<T> {
+  [Symbol.iterator](): Iterator<T>
+  at(index: number): Nullable<T>
+  atOrDefault(index: number, defaultValue: T): Nullable<T>
+  atOrElse(index: number, defaultValue: () => T): Nullable<T>
+  concat(other: IEnumerable<T>): IEnumerable<T>
+  count(): number
+  drop(limit: number): IEnumerable<T>
+  empty(): boolean
   enumerator(): IEnumerator<T>
+  every(predicate: Predicate<T>): boolean
+  filter(predicate: Predicate<T>): IEnumerable<T>
+  find(predicate: Predicate<T>): Nullable<T>
+  findIndex(predicate: Predicate<T>): number
+  flatMap<U>(fn: Morphism<T, IEnumerator<U>>): IEnumerable<U>
+  map<U>(fn: Morphism<T, U>): IEnumerable<U>
+  reduce<U>(fn: Reducer<T, U>, init: U): U
+  some(predicate: Predicate<T>): boolean
+  take(limit: number): IEnumerable<T>
+  toArray(): T[]
 }
 
 export interface IEnumeratorFactory<T> {
@@ -648,10 +666,20 @@ export class Enumerable<T> implements IEnumerable<T>, Iterable<T> {
     )
   }
 
+  count(): number {
+    return this.reduce((acc: number) => acc + 1, 0)
+  }
+
   drop(limit: number) {
     return new Enumerable(new DropEnumerator(this._enumerator, limit))
   }
 
+  empty(): boolean {
+    const next = this._enumerator.moveNext()
+    this._enumerator.reset()
+    return !next
+  }
+
   enumerator(): IEnumerator<T> {
     return this._enumerator
   }
@@ -678,6 +706,27 @@ export class Enumerable<T> implements IEnumerable<T>, Iterable<T> {
     return new Enumerable(new FilterEnumerator(this._enumerator, predicate))
   }
 
+  find(predicate: Predicate<T>): Nullable<T> {
+    const index = this.findIndex(predicate)
+    return index === -1 ? undefined : this._enumerator.current
+  }
+
+  findIndex(predicate: Predicate<T>): number {
+    let index = 0
+    let found = false
+
+    while (this._enumerator.moveNext()) {
+      if (predicate(this._enumerator.current, index)) {
+        found = true
+        break
+      }
+      index += 1
+    }
+
+    this._enumerator.reset()
+    return found ? index : -1
+  }
+
   flatMap<U>(fn: Morphism<T, IEnumerator<U>>): IEnumerable<U> {
     return new Enumerable(new FlatMapEnumerator(this._enumerator, fn))
   }
@@ -686,6 +735,18 @@ export class Enumerable<T> implements IEnumerable<T>, Iterable<T> {
     return new Enumerable(new MapEnumerator(this._enumerator, fn))
   }
 
+  reduce<U>(fn: Reducer<T, U>, init: U): U {
+    let index = 0
+    let acc = init
+
+    while (this._enumerator.moveNext()) {
+      acc = fn(acc, this._enumerator.current, index)
+    }
+
+    this._enumerator.reset()
+    return acc
+  }
+
   some(predicate: Predicate<T>): boolean {
     let index = 0
     while (this._enumerator.moveNext()) {
@@ -703,6 +764,14 @@ export class Enumerable<T> implements IEnumerable<T>, Iterable<T> {
   take(limit: number): IEnumerable<T> {
     return new Enumerable(new TakeEnumerator(this._enumerator, limit))
   }
+
+  toArray(): T[] {
+    const result = []
+    for (const item of this) {
+      result.push(item)
+    }
+    return result
+  }
 }
 
 export class ArrayEnumerble<T> extends Enumerable<T> {