Turbotax doesn't give me the option of "other" and won't let me proceed without answering, but none of the options match my situation (purchased, inherited, divorce, gift, short sale, demutualization / life insurance). These were restricted shares of my company that were given to me as incentive compensation.
Select that you purchased them. Essentially you did purchase them on the vested date. If the shares sold were used to pay federal tax (should be included in your W-2), follow the instructions below for cost basis. If you sold shares yourself later, use the actual amount paid and the amount included in your W-2. You are required to know cost basis and stocks are considered first in-first out when calculating cost basis unless you chose to sell specified shares (uncommon).
Restricted Stock Units (RSUs) is an award granted and given to high ranking employees. Rights are restricted until shares are vested. Vesting occurs after the passage of time or performance criteria are met. Shares are forfeited if the conditions are not met.