The Martingale system in online Roulette involves doubling your bet after each loss to recover previous losses with a single win. It’s primarily used on even-money bets like red/black or odd/even. While it can provide short-term wins, the system carries significant risk as extended losing streaks can lead to quickly escalating bets, potentially hitting table limits or depleting your bankroll. The Martingale doesn’t change the odds of Roulette, so its effectiveness is limited in the long run, and it requires careful bankroll management to handle potential losses.