This book aims to develop an innovative, comprehensive, integrated and empirically effective system for cross-sectionally analyzing price data of government bonds (GBs) and/or corporate bonds (CBs) with associated attribute data to timely obtain practically useful information on yield curves and default curves. The system is called K SystemK System in the sequel. And to verify the empirical effectiveness of the modeling concept, formulated models, and estimation procedures in the System from a viewpoint of data scienceData science, the models are applied to various practically important analyses on prices of Japanese GBs and CBs (JGBsGovernment Bond (GB)Japanese government bond (JGB) and JCBs), USGBsGovernment Bond (GB)US government bond (USGB) and USCBs and European GBs (EUGBs)Government Bond (GB)European government bond (EUGB) of Germany, France, Italy, Spain and Greece. All the GBs and CBs treated in this book are fixed coupon bonds of maturities longer than one year since there exists no long-term discount bond (zero-coupon bond).