Open innovation (OI) is one of the hottest topics in management literature in the past decade. According to Scopus dataset, ever since the introduction of the term in 2003, over 3600 articles have been published on the topic. Following the original definition, OI represents a new model to pursue activities where “[. . .] firms commercialize external (as well as internal) ideas by deploying outside (as well as in-house) pathways to the market”. (Chesbrough, 2003). Enkel, Gassmann, and Chesbrough (2009) distinguish three dimensions of open innovation: “outside-in”, “inside-out” and “coupled”. In particular, the outside-in (inbound) process aims at enriching the company knowledge capital by internalizing externally developed technologies. Firms search for valuable sources of knowledge in their environment, leveraging on potential sources of ideas arising from other players, i.e. suppliers, customers, competitors or universities. Drivers of acquisition of external assets include lower cost of development, lower risks and faster time-to-market (Wallin & Von Krogh, 2010). Building on the resource-based view of the firm (Barney, 1991), We join the current debate in OI literature by seeking to answer to the following question: How is inbound openness related with firm performance? So far, a number of studies focused on the effects of OI on firm performance (Chiang & Hung, 2010; Hung & Chou, 2013; Lichtenthaler, 2009). However, OI literature is yet to find consensus in defining thedeterminants of openness, as well as insorting its effect on performance. Extant studies present three main limitations in determining such relationship: first, we believe there is a bias in the measurement of firm level of openness in extant studies, since they mostly rely on self-reported measures of openness derived from secondary data. In addition, there is no consensus in the definition of what “firm performance” is in open innovation studies. Finally, results of extant studies on the relationship between inbound openness and performance are heterogeneous: multiple authors argue the presence of a positive relationship between openness and performance (Nitzsche, Wirtz, & Goettel, 2016; Rass, Dumbach, Danzinger, Bullinger, & Moeslein, 2013), while others argue there is a negative or non-linear relation between such variables (Laursen & Salter, 2006; Love, Roper, & Bryson, 2011; Suh & Kim, 2012). We seek to contribute to extant literature by proposing an empirical analysis of the effects of openness – focusing on the nature of acquired intangible assets versus internally developed assets – on firm performance, measured according to three dimensions: (1) Economic performance – through the value of turnover; (2) Financial performance – the value of firm stock prices; and (3) Human capital performance – the level of firm employment. To do so, we use an unbalanced panel data of 329 European companies listed in the five major markets – United Kingdom, Germany, France, Italy and Spain, over the period 2008–۲۰۱۳٫ Results show that the effects of both internal development and external acquisition are positive and significant across different dimensions, but their output varies in terms in magnitude and distribution: both variables are positively and significantly correlated with turnover, and their effect is almost equal. In addition, we find that only developmentis positively and significantly correlated with the other two dimensions of performance, once we control for firm-specific time trends. Once we control for relative size of firms in the sample, we see that the effect of openness is more spread out across different class sizes, while the effect of development of intangibles influences the economic performance only for larger firms, and increases employment only for relatively smaller firms, while it has no effect on the financial side of performance. The structure of the paper is the following: in the next paragraph, we will briefly review the OI literature to sort out how performance is measured by extant contributions and the direction of the relationship between openness and performance proposed by scholars. Then, we introduce the research design and methodology used in our study. In the findings section, we presentthe results of the econometric analysis. Finally, we list the article’s contributions and implications for academics and professionals in the field, we address the limitations of the study and include suggestions for further research.