Data transfer between clock domains

A system (1) for transferring a data signal (sig_fast) from a first clock domain (4) to a second clock domain (8). The first clock domain (4) has a first clock (ck_fast) with a frequency greater than the frequency of a second clock (ck_slow) in the second clock domain (8). The system (1) also has a signal input (10) for receiving an input signal (sig_fast) from the first clock domain (4), means (16, 18) for checking whether the second clock (ck_slow) is in a part of its cycle away from a forthcoming transition, and means (22) for transferring the input signal (sig_fast) to the second clock domain (8) if the checking means (16, 18) determines that the second clock (ck_slow) is in part of its cycle away from a forthcoming transition. The checking means (16, 18) are clocked by the first clock (ck_fast).