Libraries are a feature-rich set of code for a particular functionality. CodeIgnitor provides a rich set of libraries which increases the development speed of application. Default libraries can be located at system/library directory.  To Load single library please use  $this->load->library(‘class_name’); To Load multiple libraries please use $this->load->library(array(‘class_name1’, ‘class_name2’, ‘class_name3’)); Custom libraries to be created in the application/libraries directory.  If we want to add one or more methods to the existing library then it will replace the entire library with a modified version. Extending the library is a better option. There are rules to do the same.  Class declaration must extend the parent class. New class name and filename must be prefixed with MY_.classname.php