Many organisational managers often ask about the costs of well-being initiatives and whether they are worth the investment. Senior executives, including owners, directors, and especially chief financial officers, frequently want to know if spending money on employee well-being and mental health leads to real benefits. In today’s “employee market”, it’s tough for companies to attract and keep qualified staff, whether they’re managers, specialists, or even blue-collar employees, making it crucial to focus on employee well-being. However, it’s also important to evaluate the costs and potential returns of these initiatives. This chapter focuses on discussing different methods and tools for measuring employee well-being and assessing how effective and efficient well-being interventions are. It provides an overview of the theoretical background of well-being interventions at work and explores various methods and tools for evaluating the effectiveness (the degree to which the goals of the initiative are achieved) and cost-effectiveness (the ratio between costs and profits from implementing well-being interventions). These two factors can facilitate effective management of well-being initiatives and help avoid practices often referred to as “well-being washing”. In the empirical section, the chapter shares case studies from companies that have adopted well-being initiatives and discusses the methods and tools they used to evaluate their effectiveness and cost-effectiveness.