Cyber espionage has emerged as a defining threat in the contemporary digital landscape, characterized by the covert extraction of sensitive information to gain strategic, political, or economic advantage. This paper explores the critical role of Cyber Threat Intelligence in countering such threats, emphasizing its capacity to anticipate, detect, and mitigate increasingly complex adversarial campaigns. By differentiating cyber espionage from adjacent phenomena such as cybercrime and cyberterrorism, the study establishes a clear conceptual framework to address the distinct challenges posed by state-sponsored Advanced Persistent Threats. Through an in-depth case study of APT29 (Cozy Bear), a group implicated in the 2016 U.S. presidential election interference, the paper illustrates the practical application of CTI in identifying, attributing, and disrupting a sophisticated nation-state operation. The analysis highlights early detection mechanisms based on behavioral patterns, attribution through technical and contextual profiling, and coordinated responses driven by intelligence sharing. The group’s deployment of modular malware, alongside precision spear-phishing campaigns, reveals an evolving landscape shaped by stealth, persistence, and geopolitical intent. Ultimately, the case study demonstrates that effective CTI depends not only on technological capabilities, but also on institutional agility and inter-organizational cooperation. As cyber operations increasingly target democratic processes and critical infrastructure, the integration of actionable threat intelligence into strategic defense planning becomes imperative. CTI is thus positioned not merely as a reactive tool, but as a proactive instrument of resilience and national security.