Persons holding a PhD and working in public institutions (university, research centre etc.) have the right to apply for an extra taxfree income. The idea is to attract and to keep researchers in Mexico. The S.N.I. is maintained by CONACyT, e.g. the Mexican equivalent to the American NSF or German DFG.
The S.N.I. knows four levels, C (candidate), I, II, and III. The monthly income is about 600, 1000, 1350, 1800 USD (III is estimated; 13 Mexican Pesos for one USD). These values are increased yearly by about 5% to cope with the inflation.
The S.N.I. is granted for three years, but the time span may increase if a person remains in the same level. The evaluation is semi-transparent. Main focus is on papers listed in the Science Citation Index, patents, books, and contributions in meetings. Increasingly also other activities like the formation of working groups, students, classes, etc. are included for evaluation.