Memrise is based on several important scientific discoveries about how we learn. First, our system of mems (mnemonics and memory aids) promotes elaborate encoding- encouraging the learning brain to do more by engaging the imagination, and thus helping lay down stronger, more durable memories.
Secondly, Memrise makes use of Spaced Repetition, helping you review words at expertly spaced intervals to help you maintain them in memory in the most efficient manner possible. Reminders space out in time as your knowledge for a word gets deeper, meaning you don't forget, but don't waste time reviewing what you already know.
Third, Memrise systematically exploits the Testing Effect, which shows that by actively recalling a memory, you strengthen it. Because the degree of strengthening to a memory correlates with the difficulty of the test, Memrise automatically makes the tests more difficult over time, again helping you boost your learning in the best way possible.
You can find out more on the about page.