公式リンクなど
◆ Swift
https://developer.apple.com/swift/
◆ Swift Blog
https://developer.apple.com/swift/blog/

公式ドキュメント
◆ The Swift Programming Language
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/
[iBooks版] https://itun.es/i6LR9w5
◆ Using Swift with Cocoa and Objective-C
https://developer.apple.com/library/ios/documentation/Swift/Conceptual/BuildingCocoaApps/
[iBooks版] https://itun.es/i6Lr53p
◆ Swift Standard Library Reference
https://developer.apple.com/library/ios/documentation/General/Reference/SwiftStandardLibraryReference/

公式フォーラム (英語、要デベロッパーアカウント)
https://devforums.apple.com/community/tools/languages/swift