किसी घटना की व्याख्या करने वाला कोई सुझाव या अलग-अलग प्रतीत होने वाली बहुत सी घटनाओं के आपसी सम्बन्ध की व्याख्या करने वाला कोई तर्कपूर्ण सुझाव परिकल्पना (hypothesis) कहलाता है। वैज्ञानिक विधि के नियमानुसार आवश्यक है कि कोई भी परिकल्पना परीक्षणीय होनी चाहिये।

A hypothesis is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous observations that cannot satisfactorily be explained with the available scientific theories. Even though the words "hypothesis" and "theory" are often used interchangeably, a scientific hypothesis is not the same as a scientific theory. A working hypothesis is a provisionally accepted hypothesis proposed for further research in a process beginning with an educated guess or thought.