The new binary compound Gd3Ge4 has been synthesized and its structure has been determined from single-crystal X-ray diffraction. Gd3Ge4 crystallizes in the orthorhombic space group Cmcm (No. 63) with unit cell parameters a = 4.0953(11) angstrom, b = 10.735(3) angstrom, c = 14.335(4) angstrom, and Z = 4. Its structure can be described as corrugated layers of germanium atoms with gadolinium atoms enclosed between them. The bonding arrangement in Gd3Ge4 can also be derived from that of the known compound GdGe (CrB type) through cleavage of the (1)(infinity)[Ge-2] zigzag chains in GdGe and a subsequent insertion of an extra germanium atom between the resulting triangular fragments. Formally, these characteristics represent isotypism with the Er3Ge4 type (Pearson's oC28). However, re-examination of the crystallography in the whole RE3Ge4 series (RE = Y, Tb-Tm) revealed discrepancies and called into question the accuracy of the originally determined structures. This necessitated a new rationalization of the bonding, which is provided in the context of a comparative discussion concerning both the original and revised structure models, along with an analysis of the trends across the series. The temperature dependence of the magnetic susceptibility of Gd3Ge4 shows that it is paramagnetic at room temperature and undergoes antiferromagnetic ordering below 29 K. Magnetization, resistivity, and calorimetry data for several other members of the RE3Ge4 family are presented as well.