NOVELTY - An isolated polypeptide having cellulolytic enhancing activity derived from Thermomyces lanuginosus GH61 polypeptide, is new.    USE - For inhibiting the expression of a polypeptide having cellulolytic enhancing activity in a cell; for degrading or converting a cellulosic material; for fermenting cellulosic material (claimed); and for saccharifying the cellulosic material to fermentable sugars and to convert the fermentable sugars to many useful fermentation products e.g. fuel, potable ethanol, or platform chemicals such as acid, alcohol, ketone, and gas.    ADVANTAGE - The polypeptide have cellulolytic enhancing activity.    DETAILED DESCRIPTION - An isolated polypeptide having cellulolytic enhancing activity, selected from: (a) a polypeptide having at least 70% sequence identity to the mature polypeptide of sequence containing 272 amino acids (SEQ ID NO: 2) as given in the specification, or at least 60% sequence identity to the mature polypeptide of sequence containing 327 amino acids (SEQ ID NO: 4) as given in the specification, or at least 70% sequence identity to the mature polypeptide of sequence containing 274 amino acids (SEQ ID NO: 6) as given in the specification; (b) a polypeptide encoded by a polynucleotide that hybridizes under at least medium stringency conditions with (i) the mature polypeptide coding sequence of sequence containing 872 nucleic acids (SEQ ID NO: 1) as given in the specification, sequence containing 1039 nucleic acids (SEQ ID NO: 3) as given in the specification, or sequence containing 881 nucleic acids (SEQ ID NO: 5) as given in the specification, (ii) the cDNA sequence contained in the mature polypeptide coding sequence of SEQ ID NO: 1, SEQ ID NO: 3, or SEQ ID NO: 5, or (iii) a full-length complementary strand of (i) or (ii); (c) a polypeptide encoded by a polynucleotide having at least 70% sequence identity to the mature polypeptide coding sequence of SEQ ID NO: 1 and/or its cDNA sequence, or at least 60% sequence identity to the mature polypeptide coding sequence of SEQ ID NO: 3 and/or its cDNA sequence, or at least 70% sequence identity to the mature polypeptide coding sequence of SEQ ID NO: 5 and/or its cDNA sequence; (d) a variant of the mature polypeptide of SEQ ID NO: 2, SEQ ID NO: 4 or SEQ ID NO: 6 comprising a substitution, deletion, and/or insertion of at least one (e.g. several) amino acid; and (e) a fragment of the polypeptide of (a), (b), (c), or (d) that has cellulolytic enhancing activity, is new. INDEPENDENT CLAIMS are included for the following:    (1) new isolated polynucleotide encoding the polypeptide;    (2) producing (M1) the polypeptide;    (3) producing (M2) a mutant of a parent cell, involving disrupting or deleting a polynucleotide encoding the polypeptide, and/or its portion, which results in the mutant producing less of the polypeptide than the parent cell;    (4) new transgenic plant, plant part or plant cell transformed with a polynucleotide encoding the polypeptide;    (5) new double-stranded RNA (dsRNA) molecule comprising a subsequence of the polynucleotide, where optionally the dsRNA is an siRNA or an miRNA molecule;    (6) inhibiting (M3) the expression of a polypeptide having cellulolytic enhancing activity in a cell, involving administering to the cell or expressing in the cell the double-stranded RNA (dsRNA) molecule;    (7) new isolated polynucleotide encoding a signal peptide comprising or consisting of amino acids 1-22 of SEQ ID NO: 2, amino acids 1-21 of SEQ ID NO: 4, or amino acids 1-22 of SEQ ID NO: 6;    (8) producing (M4) a protein, involving: (a) cultivating a recombinant host cell comprising a gene encoding the protein operably linked to the polynucleotide, where the gene is foreign to the polynucleotide, under conditions conducive for production of the protein; and (b) recovering the protein;    (9) a composition comprising the polypeptide;    (10) degrading or converting (M5) a cellulosic material, involving: treating the cellulosic material with an enzyme composition in the presence of the polypeptide having cellulolytic enhancing activity;    (11) producing (M6) a fermentation product, involving: (a) saccharifying a cellulosic material with an enzyme composition in the presence of the polypeptide having cellulolytic enhancing activity; (b) fermenting the saccharified cellulosic material with at least one (e.g. several) fermenting microorganisms to produce the fermentation product; and (c) recovering the fermentation product from the fermentation;    (12) fermenting (M7) a cellulosic material, involving: fermenting the cellulosic material with at least one (e.g. several) fermenting microorganisms, where the cellulosic material is saccharified with an enzyme composition in the presence of a polypeptide having cellulolytic enhancing activity; and    (13) a whole broth formulation or cell culture composition comprising the polypeptide.