The phase transitions and polymorphism of three 4‐aminopyridine‐based indolocarbazole analogues are analyzed with respect to symmetry relationships and twinning. Seven polymorphs were structurally characterized using single‐crystal diffraction. 5NICz (the indolo[3,2,1‐jk]carbazole derivative with the C atom in the 5‐position replaced by N) crystallizes as a P21/a high‐temperature (270 K) polymorph and as a Pca21 low‐temperature (150 K) polymorph. Even though their space‐group symmetry is not related by a group–subgroup relationship, the local symmetries of both belong to the same order–disorder (OD) groupoid family. Both are polytypes of a maximum degree of order and are twinned by point operations of the other polytype. 2NICz (C atom in the 2‐position replaced by N) likewise crystallizes in a high‐temperature (Pcca, 280 K) polymorph and a low‐temperature (P21/c, 150 K) polymorph. Here, the space‐group symmetries are related by a group–subgroup relationship. The low‐temperature phase is twinned by the point operations lost on cooling. The crystal structure of bulk 2,5NICz (N‐substitution at the 2‐ and 5‐positions) was unrelated to 2NICz and 5NICz and no phase transition was observed. Isolated single crystals of a different polymorph of 2,5NICz, isotypic with 2NICz, were isolated. However, the analogous phase transition in this case takes place at distinctly higher temperatures (> 300 K). The phase transition behaviour and twinning of 4‐aminopyridine‐based indolocarbazoles are analyzed using the order–disorder theory and group–subgroup relationships. [ABSTRACT FROM AUTHOR]