As I continue to tinker with Scala , I was wondering about the performance differences between an Array and List. This post will detail what I've found, but as always YMMV and I could be doing it all wrong. If there's a better (in this case, better == faster) way to do this in Scala, please let me know. My application performs a lot of collection iteration as it combines the values of two collections into a new collection by addition. For instance, I need to combine [1,2] and [3,4] into [4,6] . I wanted to find out if the collections should be an Array or List. Intuition tells me that the Array will perform better, but this is Scala, and Lists reign supreme. So we'll go head to head. For each test, I wanted to write a function that combined the two collections using tail recursion. Test One - Two Lists Into a Third First up, I am adding two lists together while forming a third. One problem here is, due to the way the algorithm is structured, the resulting list is bu