One way to assess the IS and establish a foundation for improvement decisions is to evaluate its maturity using a maturity model (MM) tailored to the organization's type and the goals of these activities. The outcome is the determination of the assessed organization's maturity level, enabling the initiation of improvement activities and comparisons with similar organizations. Many such initiatives have been inspired by well-established maturity models, such as the capability maturity model (CMM). An organization with a higher level of maturity is considered more reliable and customer-friendly. This chapter delves into the issues of IS maturity, providing definitions of maturity, maturity models (with examples), models for implementing MM (change management), highlighting the distinctions and similarities between maturity, diffusion (acceptance), and innovation of information systems, as well as the relationships between methods for assessing IS maturity and the information/data literacy of its users.