Programmatically go back to previous ViewController in Swift

Swift 3

I might be late in the answer but for swift 3 you can do it this way:

override func viewDidLoad() {
    super.viewDidLoad()

    navigationItem.leftBarButtonItem = UIBarButtonItem(title: "< Back", style: .plain, target: self, action: #selector(backAction))

    // Do any additional setup if required.
}

func backAction(){
    //print("Back Button Clicked")
    dismiss(animated: true, completion: nil)
}

Swift 3:

If you want to go back to the previous view controller

_ = navigationController?.popViewController(animated: true)

If you want to go back to the root view controller

_ = navigationController?.popToRootViewController(animated: true)

If you are not using a navigation controller then pls use the below code.

self.dismiss(animated: true, completion: nil)

animation value you can set according to your requirement.

Swift 3, Swift 4

if movetoroot { 
    navigationController?.popToRootViewController(animated: true)
} else {
    navigationController?.popViewController(animated: true)
}

navigationController is optional because there might not be one.