<p>What is the most efficient way to write the old-school:</p>

<pre><code>StringBuilder sb = new StringBuilder();
if (strings.Count &gt; 0)
{
    foreach (string s in strings)
    {
        sb.Append(s + ", ");
    }
    sb.Remove(sb.Length - 2, 2);
}
return sb.ToString();
</code></pre>

<p>...in LINQ?</p>

Have you looked at the Aggregate extension method?
```
```
var sa = (new[] { "yabba", "dabba", "doo" }).Aggregate((a,b) => a + "," + b);
```
```