diff --git a/Sources/AsyncAlgorithms/Dictionary.swift b/Sources/AsyncAlgorithms/Dictionary.swift
new file mode 100644
index 00000000..f2086d92
--- /dev/null
+++ b/Sources/AsyncAlgorithms/Dictionary.swift
@@ -0,0 +1,80 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+extension Dictionary {
+  /// Creates a new dictionary from the key-value pairs in the given asynchronous sequence.
+  ///
+  /// You use this initializer to create a dictionary when you have an asynchronous sequence
+  /// of key-value tuples with unique keys. Passing an asynchronous sequence with duplicate
+  /// keys to this initializer results in a runtime error. If your
+  /// asynchronous sequence might have duplicate keys, use the
+  /// `Dictionary(_:uniquingKeysWith:)` initializer instead.
+  ///
+  /// - Parameter keysAndValues: An asynchronous sequence of key-value pairs to use for
+  ///   the new dictionary. Every key in `keysAndValues` must be unique.
+  /// - Returns: A new dictionary initialized with the elements of
+  ///   `keysAndValues`.
+  /// - Precondition: The sequence must not have duplicate keys.
+  @inlinable
+  public init<S: AsyncSequence>(uniqueKeysWithValues keysAndValues: S) async rethrows where S.Element == (Key, Value)  {
+    self.init(uniqueKeysWithValues: try await Array(keysAndValues))
+  }
+  
+  /// Creates a new dictionary from the key-value pairs in the given asynchronous sequence,
+  /// using a combining closure to determine the value for any duplicate keys.
+  ///
+  /// You use this initializer to create a dictionary when you have a sequence
+  /// of key-value tuples that might have duplicate keys. As the dictionary is
+  /// built, the initializer calls the `combine` closure with the current and
+  /// new values for any duplicate keys. Pass a closure as `combine` that
+  /// returns the value to use in the resulting dictionary: The closure can
+  /// choose between the two values, combine them to produce a new value, or
+  /// even throw an error.
+  ///
+  /// - Parameters:
+  ///   - keysAndValues: An asynchronous sequence of key-value pairs to use for the new
+  ///     dictionary.
+  ///   - combine: A closure that is called with the values for any duplicate
+  ///     keys that are encountered. The closure returns the desired value for
+  ///     the final dictionary.
+  @inlinable
+  public init<S: AsyncSequence>(_ keysAndValues: S, uniquingKeysWith combine: (Value, Value) async throws -> Value) async rethrows where S.Element == (Key, Value) {
+    self.init()
+    for try await (key, value) in keysAndValues {
+      if let existing = self[key] {
+        self[key] = try await combine(existing, value)
+      } else {
+        self[key] = value
+      }
+    }
+  }
+  
+  /// Creates a new dictionary whose keys are the groupings returned by the
+  /// given closure and whose values are arrays of the elements that returned
+  /// each key.
+  ///
+  /// The arrays in the "values" position of the new dictionary each contain at
+  /// least one element, with the elements in the same order as the source
+  /// asynchronous sequence.
+  ///
+  /// - Parameters:
+  ///   - values: An asynchronous sequence of values to group into a dictionary.
+  ///   - keyForValue: A closure that returns a key for each element in
+  ///     `values`.
+  @inlinable
+  public init<S: AsyncSequence>(grouping values: S, by keyForValue: (S.Element) async throws -> Key) async rethrows where Value == [S.Element] {
+    self.init()
+    for try await value in values {
+      let key = try await keyForValue(value)
+      self[key, default: []].append(value)
+    }
+  }
+}
diff --git a/Sources/AsyncAlgorithms/RangeReplaceableCollection.swift b/Sources/AsyncAlgorithms/RangeReplaceableCollection.swift
new file mode 100644
index 00000000..58f879e1
--- /dev/null
+++ b/Sources/AsyncAlgorithms/RangeReplaceableCollection.swift
@@ -0,0 +1,23 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+extension RangeReplaceableCollection {
+  /// Creates a new instance of a collection containing the elements of an asynchronous sequence.
+  ///
+  /// - Parameter surce: The asynchronous sequence of elements for the new collection.
+  @inlinable
+  public init<Source: AsyncSequence>(_ source: Source) async rethrows where Source.Element == Element {
+    self.init()
+    for try await item in source {
+      append(item)
+    }
+  }
+}
diff --git a/Sources/AsyncAlgorithms/SetAlgebra.swift b/Sources/AsyncAlgorithms/SetAlgebra.swift
new file mode 100644
index 00000000..884fc02b
--- /dev/null
+++ b/Sources/AsyncAlgorithms/SetAlgebra.swift
@@ -0,0 +1,25 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+extension SetAlgebra {
+  /// Creates a new set from an asynchronous sequence of items.
+  ///
+  /// Use this initializer to create a new set from an asynchronous sequence
+  /// 
+  /// - Parameter source: The elements to use as members of the new set.
+  @inlinable
+  public init<Source: AsyncSequence>(_ source: Source) async rethrows where Source.Element == Element {
+    self.init()
+    for try await item in source {
+      insert(item)
+    }
+  }
+}
diff --git a/Tests/AsyncAlgorithmsTests/TestDictionary.swift b/Tests/AsyncAlgorithmsTests/TestDictionary.swift
new file mode 100644
index 00000000..bebfc974
--- /dev/null
+++ b/Tests/AsyncAlgorithmsTests/TestDictionary.swift
@@ -0,0 +1,78 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+import XCTest
+import AsyncAlgorithms
+
+final class TestDictionary: XCTestCase {
+  func test_uniqueKeysAndValues() async {
+    let source = [(1, "a"), (2, "b"), (3, "c")]
+    let expected = Dictionary(uniqueKeysWithValues: source)
+    let actual = await Dictionary(uniqueKeysWithValues: source.async)
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_throwing_uniqueKeysAndValues() async {
+    let source = Array([1, 2, 3, 4, 5, 6])
+    let input = source.async.map { (value: Int) async throws -> (Int, Int) in
+      if value == 4 { throw NSError(domain: NSCocoaErrorDomain, code: -1, userInfo: nil) }
+      return (value, value)
+    }
+    do {
+      _ = try await Dictionary(uniqueKeysWithValues: input)
+      XCTFail()
+    } catch {
+      XCTAssertEqual((error as NSError).code, -1)
+    }
+  }
+  
+  func test_uniquingWith() async {
+    let source = [("a", 1), ("b", 2), ("a", 3), ("b", 4)]
+    let expected = Dictionary(source) { first, _ in first }
+    let actual = await Dictionary(source.async) { first, _ in first }
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_throwing_uniquingWith() async {
+    let source = Array([1, 2, 3, 4, 5, 6])
+    let input = source.async.map { (value: Int) async throws -> (Int, Int) in
+      if value == 4 { throw NSError(domain: NSCocoaErrorDomain, code: -1, userInfo: nil) }
+      return (value, value)
+    }
+    do {
+      _ = try await Dictionary(input) { first, _ in first }
+      XCTFail()
+    } catch {
+      XCTAssertEqual((error as NSError).code, -1)
+    }
+  }
+  
+  func test_grouping() async {
+    let source = ["Kofi", "Abena", "Efua", "Kweku", "Akosua"]
+    let expected = Dictionary(grouping: source, by: { $0.first! })
+    let actual = await Dictionary(grouping: source.async, by: { $0.first! })
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_throwing_grouping() async {
+    let source =  ["Kofi", "Abena", "Efua", "Kweku", "Akosua"]
+    let input = source.async.map { (value: String) async throws -> String in
+      if value == "Kweku" { throw NSError(domain: NSCocoaErrorDomain, code: -1, userInfo: nil) }
+      return value
+    }
+    do {
+      _ = try await Dictionary(grouping: input, by: { $0.first! })
+      XCTFail()
+    } catch {
+      XCTAssertEqual((error as NSError).code, -1)
+    }
+  }
+}
diff --git a/Tests/AsyncAlgorithmsTests/TestRangeReplacableCollection.swift b/Tests/AsyncAlgorithmsTests/TestRangeReplacableCollection.swift
new file mode 100644
index 00000000..ae5616e4
--- /dev/null
+++ b/Tests/AsyncAlgorithmsTests/TestRangeReplacableCollection.swift
@@ -0,0 +1,57 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+import XCTest
+import AsyncAlgorithms
+
+final class TestRangeReplacableCollection: XCTestCase {
+  func test_String() async {
+    let source = "abc"
+    let expected = source
+    let actual = await String(source.async)
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_Data() async {
+    let source = Data([1, 2, 3])
+    let expected = source
+    let actual = await Data(source.async)
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_ContiguousArray() async {
+    let source = ContiguousArray([1, 2, 3])
+    let expected = source
+    let actual = await ContiguousArray(source.async)
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_Array() async {
+    let source = Array([1, 2, 3])
+    let expected = source
+    let actual = await Array(source.async)
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_throwing() async {
+    let source = Array([1, 2, 3, 4, 5, 6])
+    let input = source.async.map { (value: Int) async throws -> Int in
+      if value == 4 { throw NSError(domain: NSCocoaErrorDomain, code: -1, userInfo: nil) }
+      return value
+    }
+    do {
+      _ = try await Array(input)
+      XCTFail()
+    } catch {
+      XCTAssertEqual((error as NSError).code, -1)
+    }
+  }
+}
diff --git a/Tests/AsyncAlgorithmsTests/TestSetAlgebra.swift b/Tests/AsyncAlgorithmsTests/TestSetAlgebra.swift
new file mode 100644
index 00000000..94acfff3
--- /dev/null
+++ b/Tests/AsyncAlgorithmsTests/TestSetAlgebra.swift
@@ -0,0 +1,50 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Async Algorithms open source project
+//
+// Copyright (c) 2021 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+//
+//===----------------------------------------------------------------------===//
+
+import XCTest
+import AsyncAlgorithms
+
+final class TestSetAlgebra: XCTestCase {
+  func test_Set() async {
+    let source = [1, 2, 3]
+    let expected = Set(source)
+    let actual = await Set(source.async)
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_Set_duplicate() async {
+    let source = [1, 2, 3, 3]
+    let expected = Set(source)
+    let actual = await Set(source.async)
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_IndexSet() async {
+    let source = [1, 2, 3]
+    let expected = IndexSet(source)
+    let actual = await IndexSet(source.async)
+    XCTAssertEqual(expected, actual)
+  }
+  
+  func test_throwing() async {
+    let source = Array([1, 2, 3, 4, 5, 6])
+    let input = source.async.map { (value: Int) async throws -> Int in
+      if value == 4 { throw NSError(domain: NSCocoaErrorDomain, code: -1, userInfo: nil) }
+      return value
+    }
+    do {
+      _ = try await Set(input)
+      XCTFail()
+    } catch {
+      XCTAssertEqual((error as NSError).code, -1)
+    }
+  }
+}