In　the　failure　of　quasi-brittle　materials　such　as　rocks,　microstuctural　damage　always　precedes　macroscopic　fracture　and　manifests　itself　in　the　formation　of　fracture　process　zones　(FPZs).　Investigations　of　the　FPZ　are　of　importance　to　a　better　understanding　of　quasi-brittle　fracture　behavior　along　with　the　size　effect　and　failure　forecast.　The　sensitivities　of　the　FPZ　to　material　microstructures,　specimen　geometries,　loading　conditions,　ambient　factors　and　monitoring　techniques　have　been　investigated　extensively,　as　well　as　the　effects　of　the　FPZ　on　crack　damage　and　strength/fracture　toughness.　The　first　purpose　in　this　study　is　to　discuss　the　developments　and　contributions　of　experimental　studies　on　the　FPZ　in　quasi-brittle　materials.　Besides,　there　is　limited　advance　knowledge　of　the　correlations　of　cracking　levels　with　the　FPZ　evolution　patterns　due　to　the　fact　that　researchers　concern　cracking　levels　seldom　from　the　FPZ　perspective.　This　study　is　also　to　establish　a　better　understanding　of　stable　and　unstable　crack　growth　in　quasi-brittle　materials　from　the　FPZ　perspective.　Acousto-optic-mechanical　data　from　uniaxial　compression　tests　faithfully　show　that　the　existence　of　apparent　FPZs　is　a　material　basis　for　unstable　crack　growth　in　flawed　granite.　©　2022　Elsevier　Ltd