How many games are there in The House of the Dead series?

Answer 1

In the main series there are the following:

1. The House of the Dead (1996)
2. The House of the Dead 2 (1998)
3. The House of the Dead III (2002)
4. The House of the Dead 4 (2005)

There are a number of spin off's too:

1. The House of the Dead 2 & 3 Return (2008)
2. The House of the Dead: EX (2009)
3. The House of the Dead: Overkill (2009)

So in all there are a total of 7 games released in the series.