A method for forming a pattern comprising: forming a film from a resist composition comprising: (a) a resin which: (i) decomposes when acted on by an acid, (ii) has a ΔSP value of 2.5 (MPa) 1/2 or above, wherein ΔSP is represented by the formula ΔSP=SP F -SP I wherein SP I represents a Hansen solubility parameter of the resin before decomposition, and SP F represents a Hansen solubility parameter of the resin after decomposition, (iii) comprises repeating units containing a lactone structure represented by any of the following general formulae (LC1-1) to (LC1-16): wherein Rb 2 represents a substituent, and n 2 represents an integer of 0 to 4; and (iv) contains 30 to 80 mol%, based on all repeating units in the resin, of a repeating unit represented by the following general formula: wherein R 1 represents a hydrogen atom, an optionally substituted methyl group or -CH 2 -R 9 wherein Rg represents a monovalent organic group, R 2 represents an alkyl group or a cycloalkyl group, and R represents an atomic group required for forming an alicyclic structure in cooperation with the carbon atom connected to R 2, (b) a compound which generates an acid when exposed to actinic rays or radiation, (c) a solvent, and (d) a hydrophobic resin; exposing the film to light; and developing the exposed film using a developer containing an organic solvent thereby forming a negative pattern. forming a film from a resist composition comprising: (a) a resin which: (i) decomposes when acted on by an acid, (ii) has a ΔSP value of 2.5 (MPa) 1/2 or above, wherein ΔSP is represented by the formula ΔSP=SP F -SP I wherein SP I represents a Hansen solubility parameter of the resin before decomposition, and SP F represents a Hansen solubility parameter of the resin after decomposition, (iii) comprises repeating units containing a lactone structure represented by any of the following general formulae (LC1-1) to (LC1-16): wherein Rb 2 represents a substituent, and n 2 represents an integer of 0 to 4; and (iv) contains 30 to 80 mol%, based on all repeating units in the resin, of a repeating unit represented by the following general formula: wherein R 1 represents a hydrogen atom, an optionally substituted methyl group or -CH 2 -R 9 wherein Rg represents a monovalent organic group, R 2 represents an alkyl group or a cycloalkyl group, and R represents an atomic group required for forming an alicyclic structure in cooperation with the carbon atom connected to R 2, (b) a compound which generates an acid when exposed to actinic rays or radiation, (c) a solvent, and (d) a hydrophobic resin; (a) a resin which: (i) decomposes when acted on by an acid, (ii) has a ΔSP value of 2.5 (MPa) 1/2 or above, wherein ΔSP is represented by the formula ΔSP=SP F -SP I wherein SP I represents a Hansen solubility parameter of the resin before decomposition, and SP F represents a Hansen solubility parameter of the resin after decomposition, (iii) comprises repeating units containing a lactone structure represented by any of the following general formulae (LC1-1) to (LC1-16): wherein Rb 2 represents a substituent, and n 2 represents an integer of 0 to 4; and (iv) contains 30 to 80 mol%, based on all repeating units in the resin, of a repeating unit represented by the following general formula: wherein R 1 represents a hydrogen atom, an optionally substituted methyl group or -CH 2 -R 9 wherein Rg represents a monovalent organic group, R 2 represents an alkyl group or a cycloalkyl group, and R represents an atomic group required for forming an alicyclic structure in cooperation with the carbon atom connected to R 2, (i) decomposes when acted on by an acid, (ii) has a ΔSP value of 2.5 (MPa) 1/2 or above, wherein ΔSP is represented by the formula ΔSP=SP F -SP I wherein SP I represents a Hansen solubility parameter of the resin before decomposition, and SP F represents a Hansen solubility parameter of the resin after decomposition, (iii) comprises repeating units containing a lactone structure represented by any of the following general formulae (LC1-1) to (LC1-16): wherein Rb 2 represents a substituent, and n 2 represents an integer of 0 to 4; and (iv) contains 30 to 80 mol%, based on all repeating units in the resin, of a repeating unit represented by the following general formula: wherein R 1 represents a hydrogen atom, an optionally substituted methyl group or -CH 2 -R 9 wherein Rg represents a monovalent organic group, R 2 represents an alkyl group or a cycloalkyl group, and R represents an atomic group required for forming an alicyclic structure in cooperation with the carbon atom connected to R 2, wherein R 1 represents a hydrogen atom, an optionally substituted methyl group or -CH 2 -R 9 wherein Rg represents a monovalent organic group, R 2 represents an alkyl group or a cycloalkyl group, and R represents an atomic group required for forming an alicyclic structure in cooperation with the carbon atom connected to R 2, (b) a compound which generates an acid when exposed to actinic rays or radiation, (c) a solvent, and (d) a hydrophobic resin; exposing the film to light; and developing the exposed film using a developer containing an organic solvent thereby forming a negative pattern.