[en] This first document describes guidelines to develop a quantification method for active pharmaceutical ingredient content in solid dose formulation, using near-infrared spectroscopy. This new approach offers several advantages over classical techniques, in particular for tablets content uniformity determination. This document is intended to help users addressing the numerous questions pertaining to number and types of samples, usable spectral range for quantification, importance of the reference method, development of a model and potential pitfalls, use of chemometrics tools and method validation. It also offers a statistical support that used as an aid for decision for routine controls, when a sample falls near acceptance limits. The document gathers basic principles and will be complemented by a second article with practical examples to illustrate the methodology.