The synthesis and single-crystal X-ray structures of hydrogen squarates of imidazole (1), histidine (2), and 2-aminopyridine (4) and squarates of histidine (3) and 4-aminopyridine (5) are reported. Both hydrogen squarate [HSQ](1-) and squarate [SQ](2-) ions participate in complementary hydrogen bonding [X-H ... O; X = N, O, or C] networks. While the [HSQ](1-) ion acts both asa donor and as an acceptor of hydrogen bonds in salts 1, 2, and 4 and creates head-to-tail infinite chains of anions in 1 and head-to-head ten-membered cyclic dimers in 4, the [SQ](2-) ion participates as a powerful acceptor of as many as six hydrogen bonds in 3 and 5. In all cases, extensive hydrogen bonding and ionic interactions between the components lead to layered assemblies. In 1, the cross-linking of the [HSQ](1-) chains by protonated imidazolium ions through N-H ... O bonds creates a two-dimensional ionic sheet which is further stabilized by the presence of C-H ... O bonds resulting from the participation of the imidazolium C-H groups. In 2 and 3, the layered structures are formed by cross-linking of the cationic self-assemblies (His-His infinite helices in 2 and His-His zigzag ribbons in 3) by [HSQ](1-) and [SQ](2-), respectively. A novel feature in 3 is the presence of two C-H ... O bonds between the more acidic CH group and the O1 in [SQ](2-). In 4, the cyclic dimers of [HSQ](1-) are interwoven into a two-dimensional sheet with a checker-board motif by the participation of 2-aminopyridinium cation in horizontal and vertical N-H ... O bonds. The two-dimensional layered assembly in 5 arises by extensive participation of water molecules in cross-linking of the alternating anion-cation conjugates both in horizontal and vertical directions. Irrespective of the presence of different types of hydrogen-bonding patterns in the structures of 1-5, the persistent formation of a two-dimensional layered assembly is significant and may be a characteristic of squaric acid salts.