Abstract: A 4-component clay-polymer-salt-water system was studied by neutron scattering. The clay-salt-water system consisted of n-butylammonium vermiculite, n-butylammonium chloride and heavy water, and the volume fraction of clay in the system was held constant, at r = 0.01. Three polymers in the molecular weight range 10,000 to 30,000 were studied, poly(vinyl methyl ether) (PVME), poly(ethylene oxide) (PEO) and poly(acrylic acid) (PAA), at a polymer volume fraction of ν = 0.01. The addition of PAA suppressed the clay swelling, irrespective of the salt concentration, c. The addition of the neutral polymers had no effect on the phase transition temperature, Tc, between the gel and tactoid phases of the system, its value remaining at 14 °C for c = 0.1 M and 30 °C for c = 0.01 M. At c = 0.01 M, the neutral polymers also had a negligible effect on the lattice constant d along the swelling axis of the clay colloid, but at c = 0.1 M, the d-value was significantly lower than in the system without added polymer. For a PVME sample of molecular weight 18,000, both d and Tc were measured as a function of ν, for volume fractions between 0 and 0.04. The addition of polymer, up to ν = 0.04, had no effect on Tc. However, even for ν values as low as 0.001, the vermiculite layers in the gel phase were more parallel and more regularly spaced than in the system without added polymer. In the gel phase, d decreased exponentially as a function of ν, from 12 nm at ν = 0 to 8 nm at ν = 0.04. In the tactoid phase, at T > 14 °C the d-value in the crystalline regions was equal to 1.94 nm at ν = 0 and ν = 0.04, showing that the spacing between the vermiculite layers is not affected by the added polymer when they are collapsed by an increase in temperature. The addition of a PVME sample of molecular weight 110,000, at ν = 0.001, had no noticeable effect on either d or Tc.