This is the era of information technology. Today the most important thing is to get the right information in right time. The users of internet and other communication technologies are increasing exponentially. Hence more and more data repositories are now being made available online information retrieval systems or search engines are used to access electronic information available on the internet. These information retrieval systems depend on the available tools and techniques for efficient retrieval of information content in response to the user query needs . Most of the work done by researchers in the field of information retrieval Systems is text oriented and monolingual. These IR systems are basically focused on English and other European languages. Due to the exponential growth in the use of internet, now we have a lot of information in the form of images, videos’ and audio form. Hence there is a need of information retrieval systems which can retrieve multimedia information as per the user’s requirements. In this chapter we will deal with the basic concepts of information retrieval systems, there needs, models of information retrieval systems and other related concepts like stemming, indexing, etc. the chapter will help scholars and young professionals to get critical information required for developing IR systems.