What is the dress code at Apple?

The dress code at Apple is casual for the most part. As with most companies, they want their programmers and engineers to be as comfortable as possible. For those working in more senior and corporate positions, business-casual is more appropriate.

For technical, engineering, or IT positions it is completely acceptable to come into work in jeans, your favorite band shirt, and sneakers. It's just as acceptable to come in wearing a three-piece suit. At the end of the day, they are most concerned with performance. As long as the clothing is work appropriate (i.e., not too short or see-through, non-offensive, and clean) then you can wear it to work.