An articulation system for chairs, the system comprising: - a frame designed to be associated with a base for a chair; - a support for a seat mounted on said frame; - at least one articulation element that is rigid and hinged to said frame so that it can rotate about an axis of rotation , wherein said support for the seat is hinged to said articulation element at a hinge point ; - a support for a backrest , distinct from said support for the seat and coupled to said articulation element; wherein the articulation system further comprises, for each side, a pin that is firmly constrained to a front portion of said frame and a slot afforded in a front portion of the support for the seat, the pin slidably engaging the slot, wherein said articulation element and said pin and slot are configured in such a manner that said articulation system takes on an at-rest configuration, in the absence of tilting forces acting upon the support for the seat and/or upon the support for the backrest, and a maximum tilting configuration in which said support for the seat is rotationally translated with respect to the at-rest configuration, said pin sliding along said slot during the transition of the articulation system from the at-rest configuration to the maximum tilting configuration and vice versa, and wherein, in a reference plane perpendicular to said axis of rotation, an angle , defined as an acute angle formed between a tangent to the slot in an instant contact point between the slot and pin and a horizontal line , above the horizontal line, faces rearward, wherein said slot has a development at least partially curvilinear, characterized in that said angle gradually increases throughout at least a portion of movement of the articulation system from the at-rest configuration to the maximum tilting configuration. - a frame designed to be associated with a base for a chair; - a support for a seat mounted on said frame; - at least one articulation element that is rigid and hinged to said frame so that it can rotate about an axis of rotation , wherein said support for the seat is hinged to said articulation element at a hinge point ; - a support for a backrest , distinct from said support for the seat and coupled to said articulation element; wherein the articulation system further comprises, for each side, a pin that is firmly constrained to a front portion of said frame and a slot afforded in a front portion of the support for the seat, the pin slidably engaging the slot, wherein said articulation element and said pin and slot are configured in such a manner that said articulation system takes on an at-rest configuration, in the absence of tilting forces acting upon the support for the seat and/or upon the support for the backrest, and a maximum tilting configuration in which said support for the seat is rotationally translated with respect to the at-rest configuration, said pin sliding along said slot during the transition of the articulation system from the at-rest configuration to the maximum tilting configuration and vice versa, and wherein, in a reference plane perpendicular to said axis of rotation, an angle , defined as an acute angle formed between a tangent to the slot in an instant contact point between the slot and pin and a horizontal line , above the horizontal line, faces rearward, wherein said slot has a development at least partially curvilinear, characterized in that said angle gradually increases throughout at least a portion of movement of the articulation system from the at-rest configuration to the maximum tilting configuration. <EOS>