Most common cause of chronic pancreatitis:
Ref. API Textbook of Medicine. Pg. 815
 
Chronic pancreatitis is a chronic inflammatory disease in which there is irreversible progressive destruction of pancreatic tissue

Its clinical course is characterized by severe pain and in the later stages, exocrine and endocrine pancreatic insufficiency .
High alcohol consumption is the most frequent cause accounting for 60-70% of case, but only 5-10%of people with alcoholism develop chronic pancreatitis . The exact mechanism remains unclear; genetic and metabolic factors may be at play.
Gallstones
Alcohol
Trauma
ERCP