Table of contents : Introduction and results....Pages 1-9 Semigroup theory....Pages 10-22 L p theory of pseudo-differential operators....Pages 23-40 L p approach to elliptic boundary value problems....Pages 41-49 Proof of Theorem 1....Pages 50-54 A priori estimates....Pages 55-60 Proof of Theorem 2....Pages 61-69 Proof of Theorem 3 - Part (i)....Pages 70-80 Proof of Theorem 3 - Part (ii)....Pages 81-104 Application to semilinear initial-boundary value problems....Pages 105-111