- The acquisition of, and failure to discard, possessions that appear to be of useless or of limited value.
- Living spaces so cluttered that using the room as intended is impossible
- Significant distress or impairment to function.
- Clinical compulsive hoarding, which is the most common type.
- OCD or 'perfectionist' hoarding.
- Animal hoarding. This is very rare, although these are the cases that reach the newspapers.
- Diogenes syndrome, also known as senile squalor syndrome is exceedingly rare disorder of self-neglect in association with severe personality disorders usually in the elderly.
Book hoarder (and the hoarding might not stop with books):