A novel soybean variety, designated 97R21 is provided. Also provided are the seeds of soybean variety 97R21, cells from soybean variety 97R21, plants of soybean 97R21, and plant parts of soybean variety 97R21. Methods provided include producing a soybean plant by crossing soybean variety 97R21 with another soybean plant, methods for introgressing a transgenic trait, a mutant trait, and/or a native trait into soybean variety 97R21, methods for producing other soybean varieties or plant parts derived from soybean variety 97R21, and methods of characterizing soybean variety 97R21. Soybean seed, cells, plants, germplasm, breeding lines, varieties, and plant parts produced by these methods and/or derived from soybean variety 97R21 are further provided.