The D'Alembert system is based on the principle made by the French mathematician Jean Le Rond'Alembert.  Is a negative progression systems were if you lose you increase the bet and if you win you decrease your bet. For example let's imagine that you're making bets of 5 units. In the first bet you win, that mean that you will have 10 units in the table. The system implied that after a winning is less chance of winning again and then I will take 5 units back and bet the 5 units left on the table. In the other hand if I lose a bet the system says that after a loss there is less chance of loss and then I will bet 2 units of 5. The strategy of this system is to try to maintain the odds in balance, not chasing losses and no risking big wins.