Sequences with zero autocorrelation are of interest because of their use in constructing orthogonal matrices and because of applications in signal processing, range finding devices, and spectroscopy. Golay sequences, which are pairs of binary sequences (i.e., all entries are \1) with zero autocorrelation, have been studied extensively, yet are known only in lengths 2 a 10 b 26 c . Ternary complementary pairs are pairs of (0, \1)-sequences with zero autocorrelation (thus, Golay pairs are ternary complementary pairs with no 0's). Other kinds of pairs of sequences with zero autocorrelation, such as those admitting complex units for nonzero entries, are studied in similar contexts. Work on ternary complementary pairs is scattered throughout the combinatorics and engineering literature where the majority approach has been to classify pairs first by length and then by deficiency (the number of 0's in a pair); however, we adopt a more natural classification, first by weight (the number of nonzero entries) and then by length. We use this perspective to redevelop the basic theory of ternary complementary pairs, showing how to construct all known pairs from a handful of initial pairs we call primitive. We display all primitive pairs up to length 14, more than doubling the number that could be inferred from the existing literature. 2001 Academic Press 1. INTRODUCTION A pair of (real-valued) sequences F=( f 1 , ..., f m );G=( g 1 , ..., g n ) is complementary, or has zero autocorrelation, if ( ff *+ gg*)(x)=w # R, ( 1 )