The Retentive Network (RetNet) has recently emerged as a formidable successor to the Transformer architecture. Although the self-attention mechanism excels at capturing global dependencies, its inherent quadratic complexity imposes significant memory constraints and inhibits scalability during long-sequence modeling. To overcome these challenges, RetNet introduces an innovative retention mechanism that integrates the inductive bias of recurrent neural networks with the parallelizable training advantages of attention-based models. This unified representation allows RetNet to achieve constant-time inference and linear-time training without sacrificing representational capacity. Despite the growing body of research demonstrating the efficacy of RetNet across diverse fields such as natural language processing, computer vision, and time-series analysis, a systematic synthesis of the current literature is currently unavailable. This paper presents the first comprehensive survey of Retentive Networks through a detailed examination of its architectural foundations, core innovations, and specialized variants. Furthermore, we provide a multi-disciplinary analysis of its applications ranging from basic sequence tasks to complex cross-modal scenarios. Finally, we offer prospective insights and suggest strategic avenues for future inquiry to facilitate the continued evolution of RetNet in both academic research and large-scale industrial applications.