When someone writes a new programming language, what do they write it IN?

Question

Please excuse my ignorance. I\'m dabbling in PHP and getting my feet wet browsing SO, and feel compelled to ask a question that I\'ve been wondering about for years:

Answer 1

A lot of languages are bootstrapped- that is written in themselves. As to why you would want to do this, it is often a good idea to eat your own dogfood.

The wikipedia article I refer to discusses the chicken and egg issue. I think you will find it quite interesting.