Your company constitution is the internal rulebook that governs how your business makes decisions, handles disputes, and manages shareholders — and getting it right from the start matters far more than most founders realise. This guide walks through what should go into a custom constitution (share transfers, director appointments, dividend policies, deadlock mechanisms), why Singapore's default Model Constitution is risky for multi-founder companies, and the formal amendment process including Special Resolution requirements and the 14-day ACRA filing deadline. Also covers the role of a company secretary and the most common mistakes: treating it as a one-time task, relying on verbal agreements, and forgetting to file amendments.