This book gives an overview on the molecular structures (MS) and crystal structures (CS) of rare earth metal (REM) complexes with a series of aminopolycarboxylic acid (APCA) ligands, which are nitrilotriacetic acid (nta), ethylenediamine-N, N, N', N'-tetraacetic acid (edta), diethylenetriamine-N, N, N', N'', N''-pentaacetic acid (dtpa), triethylenetetramine-N, N, N', N'', N''', N'''-hexaacetic acid (ttha) trans-1,2-cyclohexanediamine-N, N, N', N'-tetraacetic acid (cydta) and 1,3-propylenediamine-N, N, N', N'-tetraacetic acid (pdta). Among the REM complexes with the same APCA ligand, the coordination law (CL) of coordination numbers (CN) and geometrical conformation (GC) are discussed with emphasis. The research results indicate that the CN and GC of REM complexes with various APCA ligands mainly depend on the ionic radii and electronic configurations of central REM ions, the shape of APCA ligands as well as the category of counter ion.