Pension systems are one of the fundamental pillars of the welfare state. The ageing of the population caused by longer life expectancy and low birth rates has led to a crisis in the public pension system in developed countries. Changes for the system’s sustainability are necessary, and the scientific literature on the subject is abundant, especially in recent years. This article aims to carry out a bibliometric analysis of the research carried out to date, highlighting, in turn, future lines of research. The study was carried out on a total of 1287 articles published from 1936 to 2021 and found in the Scopus database. The SciMAT, VOSviewer, and Datawrapper tools were used to analyse the most important articles, authors, countries, and institutions by volume of production and citations, as well as the relationships between them. Likewise, the most important keywords and their evolution over time were highlighted, obtaining the main focus of the research. In addition to the general analysis, a specific study was carried out in the area of Mathematics. The results show that the leading countries are the United Kingdom, the USA, and the Netherlands. On the other hand, the lead subject area in which these articles have been published is Economics, Econometrics, and Finance. The research trends are sustainability, pension reform related to ageing, and pension insurance.