The present study is an electropalatographic and acoustic investigation of the fricatives /s, ∫/ and the affricates /ts, dz, t∫, dz/ based on data from five speakers of Majorcan Catalan and five speakers of Valencian Catalan. Results show that the articulatory characteristics of fricatives and affricates agree in several respects: the sounds traditionally labeled /∫/ and /t∫, dz/ are alveolopalatal, and are articulated at a less anterior location, are less constricted and show more dorsopalatal contact than the alveolars /s/ and /ts, dz/; the two place categories are closer to each other in Valencian than in Majorcan. Compared to voiceless affricates, voiced affricates are more anterior and more constricted, and show less dorsopalatal contact. Data also show that closure location for /t∫, dz/ occurs at the alveolar zone, and that articulatory differences among affricates are better specified at frication than at closure. Strict homorganicity between the stop and frication components of affricates appears to hold provided that constriction location at frication is compared with place of articulation at closure offset. In comparison to voiceless affricates, voiced affricates were shorter, and exhibited a longer closure and a shorter frication period, in Majorcan; in Valencian, on the other hand, closures were shortest for /dz/, and frication was systematically longer for voiceless vs. voiced affricates. These duration data appear to conform to a universal trend in Valencian but not in Majorcan where voiced affricates are lengthened intentionally. In both Catalan dialects, vowel duration varies inversely with the duration of the affricate and of its closure and frication components. The implications of these articulatory and duration characteristics for the interpretation of sound changes affecting affricates, i.e. place merging, lenition and devoicing, are discussed. © Journal of the International Phonetic Association 2007.