On closer inspection, however, we find that the scriptures upon which the vipassana revival is based (primarily the two Satipatthana-suttas and the Visuddhimagga) are often ambiguous or inconsistent, and contemporary vipassana teachers are frequently at odds with each other over the interpretation of key terms. For example, Buddhist sources categorize the range of available meditation techniques under two broad headings, samatha or ‘concentration’, and vipassana or ‘insight’.