Abstract: With the rapid development of low-altitude economy (LAE), low-altitude information networks (LAINs) must provide reliable communication, environmental sensing, and target identification to support efficient and safe airspace operation. Although integrated sensing and communications (ISAC) provides a foundation for the joint design of communication and sensing, identification must also be incorporated to meet airspace safety and regulatory requirements. This paper reviews integrated sensing, communications, and identification (ISCAI) for LAE. We first review low-altitude communication, sensing, and identification approaches and explain how representative applications motivate their integration. We then summarize low-altitude ISAC fundamentals, including system architectures, channel modeling, unified signal models, and performance metrics, followed by communication-centric and sensing-centric designs, resource allocation, and aircraft trajectory optimization. Building on these, we introduce ISCAI, focusing on a backscatter communication (BackCom)-based identification mechanism in which backscatter devices serve as electronic license plates for aircraft. We present system and signal models for integrated sensing and identification (ISAI) and ISCAI, together with multifunctional receiver designs and mutual integration gains. Finally, we discuss open problems and future directions, including an information-theoretic framework, artificial intelligence-empowered system design, and reconfigurable intelligent surface-enhanced ISCAI. This review provides a structured perspective on the evolution of LAINs toward integrated communication, sensing, and identification.