How many Skulduggery Pleasant books are there?

There is already 5 out. Skulduggery Pleasant, Skulduggery Pleasant: Playing with Fire,

Skulduggery Pleasant: The Faceless Ones, Skulduggery Pleasant: Dark Days and Skulduggery Pleasant: Mortal Coil. The 6th book is due out this month (September) and is called Skulduggery Pleasant: Death Bringer. After the 6th, there is going to be 3 more books. In conclusion: 9 books altogether

I hope this helps :)

Tanith Low