Vesting
Vesting is the mechanism by which a co-founder or employee progressively earns rights over shares or options across a defined period. It protects the company against early departure by a founder who would otherwise leave with a disproportionate share of capital.
In practice
The most common structure is four years with a one-year cliff: if the beneficiary leaves before twelve months, nothing vests; after one year, 25% is earned; the remainder unlocks monthly through to the end of the term. A co-founder who leaves at eighteen months departs with roughly 29% of their BSPCE vested, rather than the 100% they would have received by staying. Vesting aligns incentives over the long term.