This article introduces experimental methods employed to study the encoding, decoding, and acquisition of speech. The three basic types of testing paradigms that are used in infant language processing research include habituation, preference, and conditioned response. Habituation refers to the extinction of a novelty response and the preference paradigm tests whether infants show a greater response to one type of stimulus over another. The third type of infant testing paradigm is that of conditioned response, in which the infant is trained to perform some explicit behavior in response to the test stimulus. One of the infant testing methodologies is head-turn preference procedure (HPP) that been used to demonstrate that infants' memory of words also contains extralinguistic information. Another is the visual fixation procedure (VFP), in which infants control the duration of a trial by looking at a visual stimulus while they are listening to an auditory stimulus. The VFP has been used to examine infants' speech perception and the development of linguistic perceptual biases that reflect the phonetic properties of the native language. Another is intermodal preferential looking procedure (IPLP) in which the direction of an infant's eye gaze is used to make inferences about their language processing. Lastly, the switch procedure designed to study word learning, in which the infants are trained to match a sound file with a particular image.