My oldest didn't walk till 18 months. He had ear troubles - frequent ear infections can affect balance, so it all made sense later on but I was very concerned. He was also in the 90th percentile for height and weight, and some larger babies can take a bit longer to walk I was told.
Usually if they've hit about 16 months it's a good idea to check with your pediatrician. Many cases, it's nothing - and if you encourage walking, they will get it. My son had been using a push toy so he was vrooming around with that, and he'd push big trucks around too and cruising. They actually said that wasn't helping - because walking is all down to the balance (as well as strength).
Good luck :)