The need for stability in the financial and economic system arising from the outcome of the most significant of the recent financial crises was the premise for the regulation of banking capital developed by the Basel Committee. In a short time, to respond to similar needs, the European legislator has profoundly renewed the European banking regulation with the result of creating the Single Rulebook. A significant part of this harmonization tool is entrusted to Regulation 575/2013 on prudential requirements (Capital Requirement Regulation, CRR). The CRR identifies capital requirements of banks by determining the rules for the formation of bank capital and the balance ratios between the various elements of bank financing based on the riskiness of the assets. Common equity tier 1 (CET1) is one of the fundamental components of bank capital. The study sets out the structural elements of bank capital and the requisites that the capital instruments must possess in order to be classified as CET1. Furthermore, the essay highlights those profiles in which the prudential discipline overlaps the corporate one and notes those issues on which further analysis of the relationship between the disciplines could be focused.