This thesis examines the organisation of innovative activities at the firm level by proposing a conceptual framework that is built upon a survey of the recent economic literature on technical change and by applying this framework to the computer software and services industry. The objectives of the study were the following: to analyze the nature of technical change in the software industry, the sources of firms' innovation and the competencies used in the innovative activities; to focus on the relationship between internal competencies and external sources of innovation~ and to give a picture of the division of labour among firms in the innovative activities. This work proposes a conceptual framework that takes into account the interactions between technical and organisational innovations at the firm level and focuses on the innovation process as a 'division of knowledge' that involves different types of actors: individuals, with different skills, working in the same organisation, firms specialising in substitute or complementary products, users and academic research centres. The empirical analysis employed qualitative data drawn from interviews with both large a.nd small firms, and quantitative data on corporate changes of large firms (e.g., creation or shut-down of subsidiaries, launch of new producis, set up of cooperative agreements). The main results of the research can be summarised as follows. First, software firms show a cumulative, incremental pattern of product innovations and an increasing commitment to process innovations. The research shows the linkages between technical and organisational changes. Process innovations affect the retraining of software analysts-programmers and project managers, encounter obstacles in the transmission of new software engineering knowledge from the R&D department to business departments, and shape the division of tasks throughout the firm. The second research result concerns the correlation between internal skills and the firms' propensity to set up linkages with external sources of innovation. The use of generic-abstract capabilities (mathematical skills) in innovative activities make firms more open towards external channels of technical change. On the contrary, the use of context-specific capabilities (experience with the development of software applications) reduces finns' propensity to interact with external sources of technical change. Finally, there is evidence of an increasing division of labour among firms in the software industry, as indicated by the large and rising number of inter-firm cooperative agreements stipulated during the period between 1984 and 1 ?92. The analysis of inter-firm linkages and internal restructuring also points to the importance of organisational change as one dimension of the general corporate change.