We critically review our present understanding of the impact of quasi-periodic variations in axial obliquity and direction and orbital eccentricity on the climate of Mars and the relationship between these climatic changes and the occurrence of polar layered terrain. Emphasis is placed on the behavior of the seasonal cycles of dust, water, and carbon dioxide at the present epoch, as constrained by ground-based and spacecraft observations, and the modification of these cycles by the astronomical variations. We also consider the relationship between these modifications and the formation of layered terrain and discuss critical measurements and calculations that can help to resolve some of the present uncentainties. The present seasonal cycle of water is controlled by regolith adsorption and desorption, sublimation and condensation onto the permanent polar caps, and atmospheric transport. An enhanced meridional transport at times of global dust storms may be responsible for the occurence of a more extensive permanent cap and a larger annual average water vapor abundance in the northern hemisphere than in the southern hemisphere. On the longer time scales of the astronomical variations (10 5–10 6 years), exchange of water between the atmosphere and high-latitude, subsurface permafrost may also play an important role in the water cycle, in addition to the factors mentioned above. The current seasonal cycle of carbon dioxide is dominated by exchange between the atmosphere and seasonal carbon dioxide ice deposits. On longer time scales, adsorption and desorption of the subpolar regolith may help to modulate the atmospheric pressure. A key point of uncertainty is the depth of the regolith and its possible blockage by water permafrost and therefore its ability to cause large changes in atmospheric pressure. Also, it is unclear whether the perennial south cap always retains a CO 2 cover at the present epoch, although there is a limited amount of evidence that it is sometimes absent. Injection of dust into the atmosphere occurs throughout the Martian year, but it is greatest at times close to orbital perihelion and summer solstice in the southern hemisphere. The dust cycle influences the H 2O and CO 2 cycles most strongly by contributing dust particles to the polar ice deposits, which significantly lower their albedo and therefore impact their stability. Key areas of uncertainty include the fraction of airborne dust deposited in the polar regions, where the laminae beside, and the physical processes responsible for the growth and especially the decay of global dust storms. At times of low obliquity, permanent CO 2 caps form, the atmospheric pressure drops sharply, dust storm activity is severely curtailed or eliminated, and water is deposited onto the permanent caps at the expense of the regolith and permafrost reservoirs. During periods of high obliquity, no perennial CO 2 polar caps occur, water is pumped out of the polar regions, and dust loading increases over its present value if the regolith is capable of significantly elevating the atmospheric pressure. Eccentricity variations and axial precession are particularly effective in modulating the climate at times of intermediate axial obliquity. For conditions of low eccentricity and intermediate axial obliquity, hemispherical asymmetries tend to be eliminated, dust loading decreases somewhat, and more water is sublimated from both polar caps than fro the north cap for the present epoch. The layered nature of the polar laminae are due to a depth-dependent susceptibility to erosion, which, in turn, is due to astronomically induced modulations in the amounts and relative proportions of airborne dust and water ice deposited in the polar regions. Key questions include the proportion of dust and water ice in the laminae and its variation within individual layers; the relative importance of older laminae and lower-latitude material as sources of new laminae; and the factors responsible for the great youth of the laminated terrain (e.g., do troughs within the laminae propagate laterally, thus burying craters?).