A process in which you “earn” your stock overtime. The purpose of vesting is to grant stock to people over a fixed period of time so they have an incentive to stick around. A typical vesting period for an employee or Founder might be 3 – 4 years, which would mean they would earn 25% of their stock each year over a 4 year period. If they leave early, the unvested portion returns back to the company.2