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Structural materials, in addition to bearing load, are being sought to perform other functions such as enforcing mechanical compatibility between materials, heat exchange and crash energy absorption. Such needs have led to the development of multifunctional materials, notable among these, and those studied in this research, being compositionally and functionally graded materials (FGM's) and cellular metals. FGM's can be used to reduce thermal expansion mismatch between two materials such as a functional coating and a load-bearing substrate. In such cases, the deformation and creep behavior of the composite interlayers between the two materials becomes of interest. To study this aspect, composites of typical FGM materials, a nickel base superalloy and zirconia, were fabricated by powder metallurgy. It was found that zirconia reacted with Y' (Ni3Al) to form alumina and introduced elemental zirconium and oxygen into the superalloy matrix. These changes resulted in greater strengthening than that expected from composite theory at lower creep rates. At higher creep rates, though, weakening of the composites relative to the original alloy was observed. For the part of research directed toward cellular structures, techniques were developed to fabricate hexagonal honeycomb structures and a bonded woven wire mesh structure. High temperature deformation properties of the honeycomb structures in the transverse (in-plane) direction were investigated. Differences in elastic and anelastic behavior and creep strengths from those observed in solid materials are attributed mainly to the open nature of the structures. Creep in the honeycombs is characterized by cycles of primary, secondary and tertiary stages caused by shear instability in layers of cells. Room temperature tests on the woven wire bonded structure showed sharp yielding in tension but gradual yielding and higher strength in compression. Thermal expansion behavior of some cellular structures was studied since it is of interest in material compatibility. It was learned that in addition to the actual geometry of design, defects such as lack of bonding between metal constituents and residual stresses can alter thermal expansive behavior of these materials. These factors in turn can be used as a means to control thermal expansion.