 <p>A relative path is specified like this:</p> <pre><code>System.IO.File.ReadAllLines("myfile.txt"); </code></pre> <p>which will search <code>myfile.txt</code> relative to the working directory executing your application. It works also with subfolders:</p> <pre><code>System.IO.File.ReadAllLines(@"sub\myfile.txt"); </code></pre> <p>The <code>MapPath</code> function you are referring to in your question is used in ASP.NET applications and allows you to retrieve the absolute path of a file given it's virtual path. For example:</p> <pre><code>Server.MapPath("~/foo/myfile.txt") </code></pre> <p>and if your site is hosted in <code>c:\wwwroot\mysite</code> it will return <code>c:\wwwroot\mysite\foo\myfile.txt</code>.</p>