The main focus of this collection of peer-reviewed articles is biohydrometallurgy. This is the field of microbial ecology which is the key to answering central questions concerning not only the diversity and behavior of micro-organisms in commercial operations, but also possible applications in biohydrometallurgy of extremophiles coming from very different environments. The 134 papers are grouped as follows: Chapter 1: Microbial Ecology, Geomicrobiology and Bioprospecting in Natural and Mining Environments; Chapter 2: Omics, Molecular Genetics and Biochemistry of Microorganisms in Mining Proce