R package trioGxE: A data smoothing approach to explore and test gene-environment interaction in case-parent trio data. The package contains functions that 1) estimates gene-environment interaction between a SNP and a continuous non-genetic attribute by fitting a generalized additive model to case-parent trio data, 2) produces graphical displays of estimated interaction, 3) performs permutation test of gene-environment interaction; 4) simulates informative case-parent trios.