Summary: In this paper we study the notion of equivariant forms introduced in the authors’ previous works [Int. J. Number Theory 8, No. 4, 963–981 (2012; Zbl 1251.11024); Geom. Dedicata 160, 373–414 (2012; Zbl 1347.11040)]. In particular, we completely classify all the equivariant forms for a subgroup of \(\mathrm{SL}_2(\mathbb{Z})\) by means of the cross-ratio, the weight 2 modular forms, the quasimodular forms, as well as differential forms of a Riemann surface and sections of a canonical line bundle.