RNase III endonucleases cleave double-stranded RNA, transforming precursor RNAs into mature RNAs that act in pre-mRNA splicing, RNA modification, translation, gene silencing, and the regulation of developmental timing. The structure of endonuclease domain, determined, by author, in 2001, provided, first time after 33 years from first isolation of the enzyme, a hint at how this family of ribonucleases functions. First structure of full-length, unligated RNase III, was solved in 2002. First structure of full-length enzyme in complex with dsRNA was solved, by author, in 2004. After that, a significant number of RNase III structures in complex with dsRNA variants were determined. The \'key\' structure is an enzyme-product complex, published in Cell in 2006. The following years resulted in determination of the large variety of RNase III structures: from different organisms, in form of a complex with different dsRNAs, metal ions, and/or other entities. All these structures constitute a set of snapshots of the mechanism of double-stranded RNA processing by the enzyme. \r\nThis presentation is dedicated to Professor Wojciech J. Stec on the occasion of his 75th birthday. Financial support by the Polish National Science Center (NCN), grant No. DEC-2012/05/B/ST4/00075, is gratefully acknowledged.\r\n