The way firms innovate has notably changed in recent years. A clear example is the manufacturing sector which has been experiencing a new revolution in production and innovation. Linked to this industrial shift, manufacturing firms have been adopting more open and collaborative practices to innovate. This phenomenon, known as Open Innovation (OI), is helping firms to acquire and explore knowledge from external sources (inbound process) and to exploit knowledge via the commercialisation of ideas and technology (outbound process). Even though numerous researchers have studied the adoption of OI and its relation to numerous strategic and organisational results, very few studies have focused on investigating the positive influence of diverse OI approaches and practices on multiple dimensions of firm performance from different angles. These drawbacks hinder the diffusion of OI practices and raise the question of whether it is convenient for any firm in any industry to adopt or not to adopt OI. Thus, this thesis helps to fill this gap by examining the extent to which OI practices are adopted by firms and other actors in unexplored mature manufacturing industries and by understanding the unidentified roles that these practices play in relation to different dimensions of firm and industrial performance. This thesis brings together different methodologies and data to investigate OI practices with a novel multi-perspective approach. Hence, OI practices are framed within the industrial context of manufacturing firms in Italy and Sweden, several actors in the food industry, small and medium-sized enterprises (SMEs) from the Italian foundry industry, and also within worldwide SMEs designing and producing supercars. More specifically, using data from 247 European manufacturing firms collected through a tailored OI survey, this thesis supports the relevance of internal context characteristics such as firm size and provides evidence of the relation between configurations of OI models and innovation performance. Through two case studies in the food industry, this thesis demonstrates novel forms of OI practices that can be characterised and adopted by different innovation actors within and around this mature industry. Likewise, drawing from 30 rigorous case studies of small and medium-sized foundries, this research for the first time illuminates the relation between the aggregations of some innovation practices (specifically internal R&D and inbound OI) with a contemporarily relevant dimension of environmental and industrial performance such as energy efficiency.Although foregrounding the practical implications of adopting OI practices, this project also investigates and attempts to contrast some of the theoretical perspectives used when researching OI in mature manufacturing industries. This thesis concludes with an integrative study of the main aspects of the research project to demonstrate the advantages of using a multi-perspective approach to study OI. This last study, originally inspired from two case studies of small carmakers, involved collecting data from 48 small and medium-sized manufacturers of supercars with a survey designed to evaluate OI influence on several types of firm performance. Collectively, the results from this thesis confirm the validity of OI in new research contexts and reveal a combined influence of specific innovation practices on innovativeness, but also on the dimensions of industrial, environmental, and social performance. This thesis contributes to theory and practice by empirically showing that even though OI and the results of practicing it are highly context dependent, adopting OI practices can definitely have a positive influence in the overall performance of firms in mature manufacturing industries, including SMEs and other small actors.