Chein:
If you look in the Shulchan Aruch, there is no requirement to wear tzitzis unless one is wearing a four cornered garment. However, the shulchan aruch goes on to explain that since it is a minhag Yisroel to wear tzitzis all the time, one should (but again, one is NOT obligated to wear tzitzis unless he is wearing a four cornered garment).