This guide presents Keyfactor's PKI Maturity Model (PKIMM), which serves as a framework for organizations to assess and enhance their public key infrastructure (PKI) capabilities. The document outlines the importance of PKI as a foundational element for establishing trust in digital communications and operations. It explains the challenges organizations face in managing PKI, including the lack of skilled personnel and the complexity introduced by diverse PKI solutions. The guide details the five levels of PKI maturity, ranging from Ad Hoc to Resilient, and describes the critical capabilities necessary for effective PKI management, including reliability, security, efficiency, governance, agility, and strategy. Additionally, it emphasizes the need for a continuous improvement approach to PKI maturity, highlighting that organizations must adapt to evolving threats and technologies to maintain trust and operational effectiveness. This guide aims to help organizations develop a strategic approach to PKI that aligns with their business needs and future growth.