An articulation mechanism for chairs, comprising: - a frame designed to be associated with a base for a chair; - a support for a seat-backrest body; - a first and a second articulation system arranged in a rear and front portion of said frame, respectively, and configured to secure said support to said frame in an articulated manner, wherein said articulation mechanism does not have a backrest support element distinct from said support for the seat-backrest body, wherein said first and second articulation system are configured in such a manner that said articulation mechanism takes on an at-rest configuration, in the absence of tilting forces acting upon the support, and a maximum tilting configuration in which said support is roto-translated with respect to the at-rest configuration, wherein said second articulation system comprises, for each side of said articulation mechanism, a first slot afforded in either one of said support and said frame and a first pin firmly constrained to the other of said support and said frame, wherein the first pin engages said first slot in such a manner that said first pin slides in said first slot during the transition of the tilting mechanism from the at-rest configuration to the maximum tilting configuration and vice versa, wherein, in a reference plane perpendicular to said first pin, a first angle, defined as an acute angle formed between a tangent to the first slot in an instant contact point between the first slot and first pin and a horizontal line, and above the horizontal line, faces rearward, wherein the articulation mechanism comprises at least one elastic element operatively interposed between said frame and said support, wherein said elastic element abuts, at a first end thereof, against a pin firmly constrained to the frame in a front-lower portion of the frame, and at a second end thereof, against said first articulation system or against a pin solidly constrained to said support and interposed, in said reference plane, between said first and second articulation system. - a frame designed to be associated with a base for a chair; - a support for a seat-backrest body; - a first and a second articulation system arranged in a rear and front portion of said frame, respectively, and configured to secure said support to said frame in an articulated manner, wherein said articulation mechanism does not have a backrest support element distinct from said support for the seat-backrest body, wherein said first and second articulation system are configured in such a manner that said articulation mechanism takes on an at-rest configuration, in the absence of tilting forces acting upon the support, and a maximum tilting configuration in which said support is roto-translated with respect to the at-rest configuration, wherein said second articulation system comprises, for each side of said articulation mechanism, a first slot afforded in either one of said support and said frame and a first pin firmly constrained to the other of said support and said frame, wherein the first pin engages said first slot in such a manner that said first pin slides in said first slot during the transition of the tilting mechanism from the at-rest configuration to the maximum tilting configuration and vice versa, wherein, in a reference plane perpendicular to said first pin, a first angle, defined as an acute angle formed between a tangent to the first slot in an instant contact point between the first slot and first pin and a horizontal line, and above the horizontal line, faces rearward, wherein the articulation mechanism comprises at least one elastic element operatively interposed between said frame and said support, wherein said elastic element abuts, at a first end thereof, against a pin firmly constrained to the frame in a front-lower portion of the frame, and at a second end thereof, against said first articulation system or against a pin solidly constrained to said support and interposed, in said reference plane, between said first and second articulation system.