Observation in the natural sciences is an act or instance of noticing or perceiving and the acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the perception and recording of data via the use of scientific instruments. The term may also refer to any data collected during the scientific activity. Observations can be qualitative, that is, the absence or presence of a property is noted and the observed phenomenon described, or quantitative if a numerical value is attached to the observed phenomenon by counting or measuring.

किसी सजीव प्राणी द्वारा अपने ज्ञानेन्द्रियों (senses) के द्वारा अथवा किसी अन्य कृत्रिम उपकरण द्वारा बाह्य जगत का ज्ञान प्राप्त करना प्रेक्षण (Observation) कहलाता है। प्रेक्षण की क्रिया में संकलित आंकड़ों को भी 'प्रेक्षण' कहते हैं। प्रेक्षण वैज्ञानिक विधि का प्रमुख अंग है।