Based upon an analysis of pottery excavated from the Guarumal and Punta Brava archaeological sites in south coastal Ecuador, the author seeks to place these sites into an overall cultural and chronological framework within the timescale 300 BC - AD 300, and to use some of the issues deriving from a discussion of the material and the occupation of the sites to assess the validity of the Jambeli culture, as defined by Estrada, Keggers and Evans (1964). "All Jambeli Phase sites are shell middens ..." (ibid: 486) is one of the assertions questioned in this thesis, together with the question of using white-on-red decorated pottery as a distinguishing feature of the Ecuadorian Regional Developmental Period. Some of the material described as being of the Jambeli culture is likely to have been misidentified and wrongly ascribed pottery deriving from late Formative period cultures in the area, of which the most important is the Guayaquil phase, from the Gulf of Guayaquil. A clear sequence of development of pottery forms and styles can be demonstrated for the site Guarumal, from late Formative period Chorrera-like antecedents, exhibiting certain similarities with the Pechiche culture, through to those more typical of the Regional Developmental period - which is the Jambeli culture in this area - in the later phases of occupation. Stylistic parallels with several contemporary cultures in southern Ecuador (and parts of northern Peru) are also examined, for the insights or challenges they offer to questions of cultural relationships and interactions over a wider geographical area. It is increasingly clear that a re-evaluation of the Jambeli culture is necessary to take account of archaeological research of the last twenty years, research which has shown that the Jambeli culture was not merely a coastal adaptation of shell-fishing communities, but that it strecthed well into the interior and had Formative period roots.