An important topic in international business (IB) has recently been the expansion of firms from institutionally and economically less developed countries to more advanced economies [e.g. De Beule, Elia, Piscitello, 2013]. A lot of academic attention has been devoted to the peculiarity of these firms' strategies as compared to traditional multinational enterprises (MNEs). Specifically, the motives of establishing subsidiaries in more advanced contexts have been studied in the past [e.g. Chen, Li, Shapiro, 2012]. Given the surge of upmarket investments, it is the strategic asset-seeking motivation that has recently gained on relevance and, consequently, academic attention [e.g. Luo, Tung, 2007; Buckley et al., 2008]. This asset-augmenting focus, particularly discussed in the context of Chinese firms' foreign expansion through mergers and acquisitions (M&A), can be associated with resource disadvantages related to their status of latecomers to the international economy. However, the evidence on the expansion of firms from post-transition economies from the region of Central Eastern Europe (CEE) into more advanced economies and the ways in which these firms build up legitimacy in order to survive and develop in those markets, still remains scarce [Trąpczyński, Banalieva, 155 2016]. This stays in contrast with the actual relevance of Germany as a host country for Polish investment, whereby it was the second largest destination for FDI outflows in 2019 with EUR 266.4 million [Narodowy Bank Polski, 2020]. From the perspective of institutional theory, the entry of emerging market firms into more advanced markets raises a number of challenges related to achieving legitimacy in the host country and therefore ensuring sustained performance. This chapter aims to explore the methods of building legitimacy by post-transition economy firms in a more advanced economy on the example of Polish firms in Germany, and the considerations are preliminary in nature. (fragment of text)