Can you write off the spare bedroom where you answer emails as a business expense? What about the beach condo you rent out for a few weeks but use yourself all summer? The tax code draws careful lines between genuine business costs and personal living expenses—because if it didn’t, nearly every room and vacation home could become a tax shelter. This chapter walks through three big boundaries: the home office deduction, vacation home rental rules, and the hobby loss limit. By the end, you’ll know exactly when a deduction is allowed and when the IRS says, “Sorry—this one is personal.”