The presence of multifaceted physiological and anatomical barriers substantially impedes ocular drug delivery efficacy. The dynamic and static barriers at the ocular surface significantly limit drug penetration and retention, leading to bioavailability of less than 5% for traditional eye drops. Moreover, posterior segment diseases require invasive intravitreal injections for treatment, which carry high risks with poor patient compliance. In situ hydrogels, as innovative drug delivery systems, trigger a stimuli-responsive sol-gel phase transition through temperature, ionic strength, or pH. They combine the convenience of drops with long-lasting sustained-release characteristics, demonstrating great potential in ocular drug delivery. This chapter introduces the response mechanisms of different types of in situ hydrogels, representative excipients, evaluation standards for ocular in situ hydrogels, and their clinical applications. Additionally, key implementation barriers and innovative development vectors are rigorously analyzed.