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Discoveries of intrinsic two-dimensional (2D) ferromagnetism in van der Waals (vdW) crystals provide an interesting arena for studying fundamental 2D magnetism and devices that employ localized spins^{, , –}. However, an exfoliable vdW material that exhibits intrinsic 2D itinerant magnetism remains elusive. Here we demonstrate that Fe₃GeTe₂ (FGT), an exfoliable vdW magnet, exhibits robust 2D ferromagnetism with strong perpendicular anisotropy when thinned down to a monolayer. Layer-number-dependent studies reveal a crossover from 3D to 2D Ising ferromagnetism for thicknesses less than 4 nm (five layers), accompanied by a fast drop of the Curie temperature (T_C) from 207 K to 130 K in the monolayer. For FGT flakes thicker than ~15 nm, a distinct magnetic behaviour emerges in an intermediate temperature range, which we show is due to the formation of labyrinthine domain patterns. Our work …