  Charge-ordering phenomena have been highly topical over the last few years. A
phase transition towards a charge ordered state has been observed
experimentally in several classes of materials. Among them, many studies have
been devoted to the family of quasi-one dimensional organic charge-transfer
salts (TMTTF)$_2$X, where (TMTTF) stands for tetramethyltetrathiafulvalene and
X for a monovalent anion (X = PF$_6$, AsF$_6$ and SbF$_6$). However, the
relationship between the electron localization phenomena and the role of the
lattice distortion in stabilizing the charge-ordering pattern is poorly
documented in the literature. Here we present a brief overview of selected
literature results with emphasis placed on recent thermal expansion experiments
probing the charge-ordering transition of these salts.
