Pay-to-play (P2P) means that the MMO requires a monthly subscription fee or other ongoing fee in order to continue playing the game. It may also require an up-front purchase of the game in addition to the monthly subscription fee, though many of these up-front purchases include a month of game time. This was once the most common way for MMOs to finance themselves, but has fallen out of favor in recent years as an increasing number of games have switched to other business models due to difficulty in retaining a stable playerbase.