To find the greatest common factor (GCF) of 12 and 30, we can list the factors of each number.
Factors of 12: 1, 2, 3, 4, 6, 12
Factors of 30: 1, 2, 3, 5, 6, 10, 15, 30
The common factors are 1, 2, 3, and 6.
The greatest of these is 6.
Therefore, the GCF of 12 and 30 is 6.