To install QUANTUM ESPRESSO from source, you need C and Fortran-95 compilers (Fortran-90 is not sufficient, but most ``Fortran-90'' compilers are actually Fortran-95-compliant). If you don't have a commercial Fortran-95 compilers, you may install the free g95 compiler: (http://www.g95.org/) or the GNU fortran compiler gfortran: (http://www.gfortran.org/). Note that both the C and the F90 compilers must be in your PATH, or else their full path must be explicitly given.
You also need a minimal Unix environment: basically, a command shell (e.g., bash or tcsh) and the utilities make, awk and sed. MS-Windows users need to have Cygwin (a UNIX environment which runs under Windows) installed: see http://www.cygwin.com/. Note that the scripts contained in the distribution assume that the local language is set to the standard, i.e. "C"; other settings may break them. Use
export LC_ALL=Cor
setenv LC_ALL Cto prevent any problem when running scripts (including installation scripts).
Instructions for the impatient:
cd espresso-4.1/ ./configure make allExecutable programs (actually, symlinks to them) will be placed in the bin/ subdirectory.
If you have problems or would like to tweak the default settings, read the detailed instructions below.