The thermal transformations of gamma-titanium phosphate, gamma-Ti(PO4)(H2PO4). 2H(2)O, have been studied using thermogravimetric analysis, differential scanning calorimetry, X-ray powder diffraction, and temperature-resolved in-situ powder diffraction. The transformation sequence goes from gamma-Ti(PO4)(H2PO4). 2H(2)O over a new partially dehydrated form gamma'-Ti(PO4)(H2PO4).(2-x)H2O (x similar to 1) to the anhydrous form beta-Ti(PO4)(H2PO4) and then through a two-step condensation process where layered titanium pyrophosphate, Ti(PO4)(H2P2O7)(0.5), is formed first and finally cubic titanium pyrophosphate TiP2O7. The dehydration of gamma-Ti(PO4)(H2PO4). 2H(2)O and the dehydroxylation/condensation process from beta-Ti(PO4)(H2PO4) to layered titanium pyrophosphate,Ti(PO4)(H2P2O7)(0.5), was followed in-situ. A new partially dehydrated phase, gamma'-Ti(PO4)(H2PO4).(2-x)H2O (x similar to 1), which forms at approximately 50 degrees C has been detected and characterized. The unit cell is monoclinic with the lattice parameters a = 23.670(1) Angstrom, b = 6.264(1) Angstrom, c = 5.036(1) Angstrom, beta = 102.41(1)degrees, and Z = 4. Layered titanium pyrophosphate, Ti(PO4)(H2P2O7)(0.5), which forms at 375 degrees C has been characterized. The unit cell is monoclinic with lattice parameters a = 16.271(3) Angstrom, b = 6.319(1) Angstrom, c = 5.122(1) Angstrom, beta = 90.59(2)degrees, and Z = 4.