The invention pertains to bicyclic heteroaryl compounds that serve as effective phosphodiesterase (PDE) inhibitors The invention also relates to compounds which are selective inhibitors of PDE-10. The invention further relates to intermediates for preparation of such compounds; pharmaceutical compositions comprising such compounds; and the use of such compounds in methods for treating certain central nervous system (CNS) or other disorders. The invention relates also to methods for treating neurodegenerative and psychiatric disorders, for example psychosis and disorders comprising deficient cognition as a symptom.