LINQ:
*LINQ
*Any
*Zip
*Min
*Cast
*All
*Sum
*Take
*Max
*Skip
*Last
*Union
*Join
var numbers1to5 = new[] {1,2,3,4,5};
var numbers4to8 = new[] {4,5,6,7,8};
var numbers1to8 = numbers1to5.Union(numbers4to8);
Console.WriteLine(string.Join(",", numbers1to8));
//1,2,3,4,5,6,7,8
Note that duplicates are removed from the result. If this is undesirable, use Concat instead.