How Can I Get the Assembly File Version

There are three versions: assembly, file, and product. They are used by different features and take on different default values if you don't explicit specify them.

string assemblyVersion = Assembly.GetExecutingAssembly().GetName().Version.ToString(); 
string assemblyVersion = Assembly.LoadFile("your assembly file").GetName().Version.ToString(); 
string fileVersion = FileVersionInfo.GetVersionInfo(Assembly.GetExecutingAssembly().Location).FileVersion; 
string productVersion = FileVersionInfo.GetVersionInfo(Assembly.GetExecutingAssembly().Location).ProductVersion;

When I want to access the application file version (what is set in Assembly Information -> File version), say to set a label's text to it on form load to display the version, I have just used

versionlabel.Text = "Version " + Application.ProductVersion;

This approach requires a reference to System.Windows.Forms.

UPDATE: As mentioned by Richard Grimes in my cited post, @Iain and @Dmitry Lobanov, my answer is right in theory but wrong in practice.

As I should have remembered from countless books, etc., while one sets these properties using the [assembly: XXXAttribute], they get highjacked by the compiler and placed into the VERSIONINFO resource.

For the above reason, you need to use the approach in @Xiaofu's answer as the attributes are stripped after the signal has been extracted from them.

public static string GetProductVersion()
{
  var attribute = (AssemblyVersionAttribute)Assembly
    .GetExecutingAssembly()
    .GetCustomAttributes( typeof(AssemblyVersionAttribute), true )
    .Single();
   return attribute.InformationalVersion;
}

(From - as noted there, if you're looking for a different attribute, substitute that into the above)

Use this:

((AssemblyFileVersionAttribute)Attribute.GetCustomAttribute(
    Assembly.GetExecutingAssembly(), 
    typeof(AssemblyFileVersionAttribute), false)
).Version;

Or this:

new Version(System.Windows.Forms.Application.ProductVersion);