<r>.NET 4+<br/>
<br/>
IList strings = new List{"1","2","testing"};<br/>
string joined = string.Join(",", strings);<br/>
<br/>
```<br/>
<br/>
**Detail & Pre .Net 4.0 Solutions**<br/>
<br/>
`IEnumerable` can be converted into a string array *very* easily with LINQ (.NET 3.5):<br/>
<br/>
```<br/>
IEnumerable strings = ...;<br/>
string[] array = strings.ToArray();<br/>
<br/>
```<br/>
<br/>
It's easy enough to write the equivalent helper method if you need to:<br/>
<br/>
```<br/>
public static T[] ToArray(IEnumerable source)<br/>
{<br/>
return new List(source).ToArray();<br/>
}<br/>
<br/>
```<br/>
<br/>
Then call it like this:<br/>
<br/>
```<br/>
IEnumerable strings = ...;<br/>
string[] array = Helpers.ToArray(strings);<br/>
<br/>
```<br/>
<br/>
You can then call `string.Join`. Of course, you don't *have* to use a helper method:<br/>
<br/>
```<br/>
// C# 3 and .NET 3.5 way:<br/>
string joined = string.Join(",", strings.ToArray());<br/>
// C# 2 and .NET 2.0 way:<br/>
string joined = string.Join(",", new List(strings).ToArray());<br/>
<br/>
```<br/>
<br/>
The latter is a bit of a mouthful though <E>:)</E><br/>
<br/>
This is likely to be the simplest way to do it, and quite performant as well - there are other questions about exactly what the performance is like, including (but not limited to) [this one](https://stackoverflow.com/questions/219519/whats-the-c-method-syntax-for-converting-an-array-to-a-simple-string).<br/>
<br/>
As of .NET 4.0, there are more overloads available in [`string.Join`](http://msdn.microsoft.com/en-us/library/system.string.join), so you can actually just write:<br/>
<br/>
```<br/>
string joined = string.Join(",", strings);<br/>
<br/>
```<br/>
<br/>
Much simpler <E>:)</E></r>
