 Dear students, in this topic we shall discuss some basic concepts of animal behavior. Animal behavior is defined as the sum total of responses made by an animal to the external and internal stimuli. The animal behavior is based on its physiological systems and processes. The scientific study of animal behavior in natural environment is studied in the branch of biology which is called ethology. Dear students, let us take few examples of animal behavior. Animals of animals may be simple. For example, moving towards or away from light, blinking of eyes and many reflex movements. However, most of animal behaviors are quite complex. For example, defense of territory, courtship and mating behaviors, liking, disliking, fighting and caring, these are also complex behaviors. Another example of complex behaviors is the migration and navigation seen in many animals. Moreover, the building of nests, hives and dens by different animals is a complex behavior. Similarly, producing meaningful voices and songs by birds and mammals is also a complex behavior. Communicating among the members of species and learning and memorizing the events that is also included in complex behaviors. Dear students, most of the behaviors are essential for the survival and reproductive success of the animals. Such behaviors which are important for survival are substantially subject to natural selection and evolution. So most of the behavioral patterns have been subject to evolution and natural selection. Dear students, nature selection may behavior key development may though major angles contribute to it. First of all, the anatomical development of the nervous system is a major angle or major line on which evolution and natural selection have operated. Secondly, the physiological features of the anatomical development of the nervous system and its physiological features enhance the advancement of the animals and the higher animals. Dear students, study of animal behavior or ethology has certain objectives. For example, to understand the stimuli that elicit behavior. To understand the physiological mechanisms which mediate response. To understand the animals' experiences that influence behavior. Mutlif animals change their behaviors based on different experiences. An ethologist studies these experiences in ethology. Ethology also involves understanding of the role of behavior in survival and reproduction. Moreover, the study of evolutionary history of behavior is also one of an important objectives of ethology.