How to join 2 or more .WAV files together programmatically?

Here’s a basic WAV concatenation function built using NAudio. This will ensure that only the data chunks are concatenated (unlike the code example in this CodeProject article linked in another answer). It will also protect you against concatenating WAV files that do not share the same format.

public static void Concatenate(string outputFile, IEnumerable<string> sourceFiles)
{
    byte[] buffer = new byte[1024];
    WaveFileWriter waveFileWriter = null;

    try
    {
        foreach (string sourceFile in sourceFiles)
        {
            using (WaveFileReader reader = new WaveFileReader(sourceFile))
            {
                if (waveFileWriter == null)
                {
                    // first time in create new Writer
                    waveFileWriter = new WaveFileWriter(outputFile, reader.WaveFormat);
                }
                else
                {
                    if (!reader.WaveFormat.Equals(waveFileWriter.WaveFormat))
                    {
                        throw new InvalidOperationException("Can't concatenate WAV Files that don't share the same format");
                    }
                }

                int read;
                while ((read = reader.Read(buffer, 0, buffer.Length)) > 0)
                {
                    waveFileWriter.WriteData(buffer, 0, read);
                }
            }
        }
    }
    finally
    {
        if (waveFileWriter != null)
        {
            waveFileWriter.Dispose();
        }
    }

}