Data mining is the extraction of the valuable data from the large amount of data. There are numerous number of algorithms available for data mining. Single algorithm is not capable of producing efficient results. There is a key term in data mining known as ensemble learning which means combining two or more classifiers for the better result.I have used the KDD'99 dataset for the experiment which have 41 features labeled either as normal or as attack. In this book I have represented how the graphical tool weka can be used for data mining and how ensemble learning can be implemented using weka....