Product innovation is crucial for firms to survive and improve their overall performance in the current dynamic and competitive market (e.g., Katila, 2002; Smith, Collins, & Clark, 2005; Zhou & Wu, 2010). Specifically, following the OECD (2005), with the term product innovation, we refer to the introduction of a product in the form of a good or service that is novel with regard to the current offerings. To be effective in product innovation, firms require extensive efforts in searching and recombining knowledge. Notably, a core area of research on product innovation draws on the recombinatory search literature (Katila, 2002; Schumpeter, 1934; Grimpe & Sofka, 2009; Fleming, 2001; Savino, Messeni Petruzzelli, & Albino, 2017), which argues that searching for knowledge, while identifying original combinations between past and new knowledge components, is at the basis of product innovation activities. In particular, some studies (e.g., Kogut & Zander, 1992; Rosenkopf & Nerkar, 2001) went deeper into the recombinatory perspective of innovation, highlighting the need to go beyond the original tendency of innovating companies to search for knowledge locally (i.e., within their boundaries), especially suggesting to employ external knowledge sources. In fact, it is unlikely that all the knowledge needed to innovate can origin and reside within the firm boundaries (Enkel, Gassmann, & Chesbrough, 2009). Rather, for many companies (e.g., Procter & Gamble, Deutsche Telekom, and General Electric), the ability to source and recombine knowledge from the external environment is becoming more and more as the key to sustain internal product innovation efforts, which is in line with the recent principles of open innovation (Chesbrough, 2003; Dahlander & Gann, 2010; Saebi & Foss, 2015).

However, benefiting from external search is not an easy task. Indeed, one of the major issues lies in the fact that the number of different external sources from which firms can acquire relevant knowledge is wide, so they should determine the breadth of external knowledge sourcing that maximizes product innovation performance (Laursen & Salter, 2006). On the one hand, the attitude to rely on a wide variety of external knowledge sources (hereafter, external search breadth) allows firms to overcome cognitive myopia (Levinthal & March, 1993), explore new knowledge areas, and develop mental models that stimulate knowledge recombination in product innovation (e.g., Laursen, 2012). On the other hand, the risks of over-search [i.e., the absorptive capacity problem, the timing problem, the attention allocation problem, and the not-invented-here (NIH) syndrome] (see Katz & Allen, 1982; Koput, 1997; Laursen & Salter, 2006) can exceed the benefitsderiving from searching widely. Thus, an inverted U-shaped relationship between external search breadth and product innovation has been claimed (e.g., Laursen & Salter, 2006; Leiponen, 2012; Wu, 2014).

Despite the validity of this argument, organizations cannot themselves search, in the sense that the acquisition and exploitation of external knowledge is a task in charge of the various organizational members. Specifically, prior research (e.g., Leiponen, 2012; Van der Vegt & Janssen, 2003) underlined that the ability of firms to internalize and recombine external knowledge is strongly dependent on the implementation of organizational practices that allow their employees to engage in collective creative thinking and recombination processes. Therefore, external search breadth may be more (or less) effective depending on the firmspecific practices that each firm sets to organize knowledge workers. This recalls insights from the human resource (HR) literature (Beugelsdijk, 2008; Huselid, 1995), claiming that companies need to organize innovation activities by making use of strategic HR practices that can enhance employees’ attitude at absorbing new knowledge in a timely manner, sharing information, and paying attention to novel recombination opportunities, with the ultimate aim of achieving the desired work behaviors and efforts contributing to innovation outcomes. Accordingly, it has been proposed that “organizational practices for managing innovation within the firm’s boundaries are facilitators of external knowledge sourcing activities as they aim for successful mobilization and application of knowledge” by the firm’s employees (Brunswicker & Vanhaverbeke, 2015, p. 1243, Batisti
c,
Cerne, Ka
se & Zupic, 2016). Nonetheless, to the best of our knowledge, no empirical research has been conducted to elucidate whether and how the adoption of HR practices influences the relationship between external search strategies and product innovation.