Travel expenses are the ordinary and necessary expenses of traveling away from home for your business, profession, or job. Generally, employees deduct these expenses using Form 2106 (PDF) or Form 2106-EZ (PDF) and on Form 1040, Schedule A (PDF). You cannot deduct expenses that are lavish or extravagant or that are for personal purposes.

You are traveling away from home if your duties require you to be away from the general area of your tax home for a period substantially longer than an ordinary day’s work, and you need to get sleep or rest to meet the demands of your work while away.

via Tax Topics – Topic 511 Business Travel Expenses.