Book excerpt: This textbook will familiarize readers with some of the most pressing solidarity and social justice issues in contemporary societies. Ongoing and emerging inequalities along the lines of gender, age, socio-economic status, ethnic background, and sexual orientation challenge the solidarity underlying societies, resulting in complex questions of social justice. Moreover, several global challenges, such as digitalization, climate change, and the COVID-19 pandemic challenge solidarity and social justice in new ways. How do societies respond to these enduring, growing or changing inequalities? Do these challenges lead to an expansion or an erosion of solidarity, in an 'us versus them' rhetoric? And to what extent do societies differ in their social justice values and hence the acceptance of social inequality? Taking a sociological, psychological, and political philosophical approach to these topics, this book offers state-of-the art theoretical and empirical contributions from globally-recognized scholars in sociology, psychology, and political philosophy, providing a unique interdisciplinary approach to understanding solidarity and social justice in response to social inequalities in contemporary European societies.