During the COVID-19 pandemics, sensitive and reliable assays for SARS-CoV-2 detection are essential for screening the population, identifying asymptomatic individuals, making diagnoses, monitoring treatment responses, and determining viral clearance. This review summarizes the principles, advantages, disadvantages, and specific applications of currently available assays for detection of the viral nucleotide, genome or proteins, as well as host antibody responses, and provide overall guidelines for selection of optimal assays for specific usage.