Reference types store an address of their data, aka “pointer” on the portion of the memory called the “stack”. The actual data to which the pointer refers to is stored in an area of memory called the “heap”. Because reference types directly store the address “pointer” to the data rather than the data itself, assigning one reference variable to another doesn’t copy the data over. Instead, it merely creates a second copy of the “pointer”, which also refers to the same memory on the heap as the original.