This invention includes methods of forming trench isolation. In one implementation, isolation trenches are provided within a semiconductor substrate. A liquid is deposited and solidified within the isolation trenches to form a solidified dielectric within the isolation trenches. The dielectric comprises carbon and silicon, and can be considered as having an elevationally outer portion and an elevationally inner portion within the isolation trenches. At least one of carbon removal from and/or oxidation of the outer portion of the solidified dielectric occurs. After such, the dielectric outer portion is etched selective to and effective to expose the dielectric inner portion. After the etching, dielectric material is deposited over the dielectric inner portion to within the isolation trenches.