Playwright that is hosting book society (Norway) (5)
I believe the answer is:
ibsen
'playwright' is the definition.
(I know that Ibsen is a playwright)
'that is hosting book society norway' is the wordplay.
'that is' becomes 'ie' (short for Latin 'id est', 'that is').
'hosting' means one lot of letters goes inside another (inserted letters are welcomed in or hosted).
'book' becomes 'b' (abbreviation for book).
'society' becomes 's' (common abbreviation in names of organisations).
'norway' becomes 'n'.
'b'+'s'='bs'
'ie' enclosing 'bs' is 'ibse'.
'ibse'+'n'='IBSEN'
(Other definitions for ibsen that I've seen before include "See 7 Down" , "Author of The Master Builder, d. 1906" , "'Doll's House' playwright" , "Norse playwright" , "famous Norwegian" .)