A method of increasing the activity of a GH61 family polypeptide having cellulolytic enhancing activity, comprising: adding a soluble activating divalent metal cation selected from the group consisting of Mn++, Co++, Mg++, Ca++, and a combination thereof, to a composition comprising the GH61 family polypeptide having cellulolytic enhancing activity, wherein the soluble activating divalent metal cation is present at an effective concentration of preferably about 0.001 mM to about 50 mM, more preferably about 0.01 mM to about 25 mM, more preferably about 0.1 mM to about 25 mM, more preferably about 0.1 mM to about 10 mM, even more preferably about 0.3 mM to about 5 mM, most preferably about 0.3 mM to about 2.5 mM, and even most preferably about 0.3 mM to about 1 mM during degradation or conversion of a cellulose-containing material and the presence of the soluble activating divalent metal cation and the polypeptide having cellulolytic enhancing activity increases the degradation or conversion of the cellulose-containing material by a cellulolytic enzyme composition compared to the polypeptide having cellulolytic enhancing activity without the soluble activating divalent metal cation, wherein the GH61 family polypeptide having cellulolytic enhancing activity is selected from the group consisting of: (a) a GH61 family polypeptide having cellulolytic enhancing activity comprising [ILMV]-P-X(4,5)-G-X-Y-[ILMV]-X-R-X- -X - and - -K-, wherein X is any amino acid, X(4,5) is any amino acid at 4 or 5 contiguous positions, and X is any amino acid at 4 contiguous positions; and (b) a GH61 family polypeptide having cellulolytic enhancing activity comprising [ILMV]-P-x(4,5)-G-x-Y-[ILMV]-x-R-x- -x -A-, wherein x is any amino acid, x(4,5) is any amino acid at 4 or 5 contiguous positions, and x is any amino acid at 3 contiguous positions; wherein the polypeptide having cellulolytic enhancing activity comprising [ILMV]-P-X(4,5)-G-X-Y-[ILMV]-X-R-X- -X - and - -K- optionally further comprises: H-X(1,2)-G-P-X - -[AILMV], -X-Y-X -C-X-[EHQN]-[FILV]-X-, or H-X(1,2)-G-P-X - -[AILMV] and -X-Y-X -C-X-[EHQN]-[FILV]-X-, wherein X is any amino acid, X(1,2) is any amino acid at 1 position or 2 contiguous positions, X is any amino acid at 3 contiguous positions, and X is any amino acid at 2 contiguous positions. (a) a GH61 family polypeptide having cellulolytic enhancing activity comprising [ILMV]-P-X(4,5)-G-X-Y-[ILMV]-X-R-X- -X - and - -K-, wherein X is any amino acid, X(4,5) is any amino acid at 4 or 5 contiguous positions, and X is any amino acid at 4 contiguous positions; and (b) a GH61 family polypeptide having cellulolytic enhancing activity comprising [ILMV]-P-x(4,5)-G-x-Y-[ILMV]-x-R-x- -x -A-, wherein x is any amino acid, x(4,5) is any amino acid at 4 or 5 contiguous positions, and x is any amino acid at 3 contiguous positions; wherein the polypeptide having cellulolytic enhancing activity comprising [ILMV]-P-X(4,5)-G-X-Y-[ILMV]-X-R-X- -X - and - -K- optionally further comprises: H-X(1,2)-G-P-X - -[AILMV], -X-Y-X -C-X-[EHQN]-[FILV]-X-, or H-X(1,2)-G-P-X - -[AILMV] and -X-Y-X -C-X-[EHQN]-[FILV]-X-, wherein X is any amino acid, X(1,2) is any amino acid at 1 position or 2 contiguous positions, X is any amino acid at 3 contiguous positions, and X is any amino acid at 2 contiguous positions. H-X(1,2)-G-P-X - -[AILMV], -X-Y-X -C-X-[EHQN]-[FILV]-X-, or H-X(1,2)-G-P-X - -[AILMV] and -X-Y-X -C-X-[EHQN]-[FILV]-X-,