In recent decades, some authors have proposed rejecting Cronbach’s alpha (α) coefficient (1951) to adopt McDonald’s omega (ω) coefficient (1985, 1999) which is based on a factor analysis model. After presenting some inherent limits of the α, this article follows two aims : (i) understanding the theoretical logic behind omega coefficients and (ii) presenting ω coefficients’ specificities regarding their computation method. To this end, we identify conditions for the use of the different forms of ω (total or hierarchical, with an EFA or CFA). An example of analysis and recommendations are suggested to better argue the score reliability.