Optofluidics　incorporates　optics　and　microfluidics　together　to　construct　novel　devices　for　microsystems,　providing　flexible　reconfigurability　and　high　compatibility.　Among　many　novel　devices,　a　prominent　one　is　the　in-plane　optofluidic　lens.　It　manipulates　the　light　in　the　plane　of　the　substrate,　upon　which　the　liquid　sample　is　held.　Benefiting　from　the　compatibility,　the　in-plane　optofluidic　lenses　can　be　incorporated　into　a　single　chip　without　complicated　manual　alignment　and　promises　high　integration　density.　In　term　of　the　tunability,　the　in-plane　liquid　lenses　can　be　either　tuned　by　adjusting　the　fluidic　interface　using　numerous　microfluidic　techniques,　or　by　modulating　the　refractive　index　of　the　liquid　using　temperature,　electric　field　and　concentration.　In　this　paper,　the　in-plane　liquid　lenses　will　be　reviewed　in　the　aspects　of　operation　mechanisms　and　recent　development.　In　addition,　their　applications　in　lab-on-a-chip　systems　are　also　discussed.　©　2018　by　the　authors.