Fatigue Crack Growth in Reliability estimates the distribution of material lifetime due to mechanical fatigue efforts. The 'FCGR' package provides simultaneous crack growth curves fitting to different specimens in materials under mechanical stress efforts. Linear mixed-effects models with smoothing B-Splines and the linearized Paris-Erdogan law are applied. Once defined the fail for a determined crack length, the distribution function of failure times to fatigue is obtained. The density function is estimated by applying nonparametric binned kernel density estimate ('bkde') and the kernel estimator of the distribution function ('kde'). The results of Pinheiro and Bates method based on nonlinear mixed-effects regression ('nlme') can be also retrieved. The package contains the crack.growth(), PLOT.cg(), IB.F(), and Alea.A (database) functions.