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The van der Waals magnet CrI₃ has been thought to host ferromagnetism in its bulk form and interlayer antiferromagnetism in its few-layer form. The magnetic excitations in bulk CrI₃ have been probed by inelastic neutron scattering, while those in CrI₃ films have been studied with inelastic magneto-tunneling spectroscopy and Raman spectroscopy. Despite such intensive effort, it remains mysterious till now how the interlayer magnetism evolves from the ferromagnetic type in bulk to the antiferromagnetic one in thin films and what the low energy magnetic excitations are in CrI₃. In this talk, we will present our results on temperature- and magnetic field-dependent resonant Raman spectroscopy studies on bulk CrI₃. We will show our experimental evidences on the complex spin wave structures in bulk CrI₃ and their intricate magnetic field dependence. We will further discuss the magnetic field dependence of phonons and explore the interplay between the lattice and the spin degrees of freedom in bulk CrI₃.