An interbody spacer for implantation into the intervertebral space between adjacent vertebrae of a patient's spinal column. The interbody spacer is a monolithic body having a predetermined slot design formed therein that provides flexibility to the spacer to allow movement of the adjacent vertebrae along multiple axies, that is, the patient can move both side to side and front to back and rotation. In one embodiment, the slot design is a spiral slot and in an alternate embodiment, the slot design comprises pairs of oppositely disposed, co-planar slots with alternating pairs of the slots offset about 90 degrees from the preceding pair of slots. Further embodiments include interbody spacers having the aforedescribed slot designs for implantation from the posterior, the anterior or translaterally into the intervertebral space while still allowing the multi-axial flexibility of the adjacent vertebrae.