The thesis analyses the case studies of three truck manufacturing firms with the purpose of contributing to the body of knowledge concerning technical change in the manufacturing sector of developing countries. This is done by a) identifying some of the factors which influence technological efforts of the three major truck manufacturing firms in Turkey, b) analysing the nature (direction) and rate of technical change in the sector, and c) examining underlying mechanisms in the process of technical change by which additional technological capabilities have been acquired and workers' contribution to this process. Such knowledge forms an essential base on which an effective technology policy and industrialisation strategy can be formulated to promote post-investment technological development within firms. Part I first draws attention to the lack of empirically based analys is of techni ca 1 change whi ch takes into account macroeconomi c conditions and inter-firm differences in examining the main aspects of technical change such as determinants, the nature and rate of change. Then it gi ves an hi stori ca 1 revi ew of the Turk ish economy and the development of the Turkish automotive industry which is greatly influenced by industrialisation policies. This macroeconomic background provi des an understandi ng of the economi c envi ronment in which the case study firms operate and enables us to evaluate their technological behaviour. Part II presents the case studies of the three Turkish truck firms. It explores the firms' characteristics and historically exami nes thei r phys i ca 1 and economi c performance, and techno 1 ogi ca 1 efforts to generate technical change. Then it explores how and to what extent the macroeconomi c condi t ions i nfl uence thei r efforts for change. Part III draws lessons from the case studies by analysing significance of industrialisation policies that greatly determine the macroeconomic conditions and their effect on determining the nature, rate and impact of techni ca 1 change. Then it gi ves an i nter-fi rm comparative analysis to identify firm level factors which are also influential in the firms' technological dynamism.