According to the invention, there is provided a novel soybean variety designated 90Y40. This invention thus relates to the seeds of soybean variety 90Y40, to the plants of soybean 90Y40 to plant parts of soybean variety 90Y40 and to methods for producing a soybean plant produced by crossing plants of the soybean variety 90Y40 with another soybean plant, using 90Y40 as either the male or the female parent.