The LCM (Least Common Multiple) of 6 and 9 is 18. The LCM is the smallest or the least positive integer that is divisible by the given set of numbers. There are different methods to find the LCM of two numbers, such as prime factorization, division method, and listing the multiples. For example, using the prime factorization method, we can express 6 and 9 as 2 x 3 and 3 x 3, respectively. Then, we take the product of the highest powers of all prime factors, which gives us 2 x 3 x 3 = 18 as the LCM of 6 and 9.