If all the cache lines in the cache are in use when the processor accesses a new line, one of the lines currently in the cache must be evicted to make room for the new line. The policy for selecting which line to evict is called the replacement policy.

The most common replacement policy in modern processors is LRU, for least recently used. This replacement policy simply evicts the cache line that was least recently used, assuming that the more recently used cache lines are more likely to soon be used again.

Another replacement policy is random replacement, meaning that a random cache line is selected for eviction.