List<string> to string

var strings = new List<string> { "blah", "de", "hoo", "ha" };

var result = strings.Aggregate((i, j) => i + " " + j); 

Console.Write(result);

And with a complex type, where a response has a collection of messages, each with a text property:

var messages = this.Response
                   .Messages
                   .Select(m => m.Text)
                   .Aggregate((i, j) => i + " " + j);