If you've got a DateTime instance, just call myDate.ToString(); you can optionally specify a format-string or predefined culture settings to get the right format (e.g. myDate.ToString("yyyy-MM-dd"); or myDate.ToString(CultureInfo.CurrentCulture); )
In .NET, every class inherits Object's .ToString() method, by default this method simply returns some basic information gained from Reflection, but some types (such as DateTime) override the behaviour. There is also the System.Convert class, but I find myself
rarely using it (since it's nothing you can't do with the existing .TryParse / .Parse / .ToString methods.