The Internet of Things (IoT) aims to transform the human society toward becoming intelligent, convenient, and efficient with potentially enormous economic and environmental benefits. Reliability is one of the main challenges that must be addressed to enable this revolutionized transformation. Based on the layered IoT architecture, this article first identifies reliability challenges posed by specific enabling technologies of each layer. This article then presents a systematic synthesis and review of IoT reliability-related literature. Reliability models and solutions at four layers (perception, communication, support, and application) are reflected and classified. Despite the rich body of works performed, the IoT reliability research is still in its early stage. Challenging research problems and opportunities are then discussed in relation to current underexplored behaviors and future new aspects of evolving IoT system complexity and dynamics.