In fiscal year 2013, Medicaid -- jointly financed by states and the federal government -- provided health care coverage to over 70 million individuals at a total cost of about $460 billion. Congress generally established Medicaid as the health care payer of last resort, meaning that if enrollees have another source of health care coverage -- such as private insurance -- that source should pay, to the extent of its liability, before Medicaid does. This is referred to as third-party liability (TPL). There are known challenges to ensuring that Medicaid is the payer of last resort. This book examines the extent to which Medicaid enrollees have private insurance; and state and Centers for Medicare & Medicaid Services (CMS) initiatives to improve TPL efforts. Provided in this book is the Effective Practices Guide. Its intent is to provide state Medicaid agencies with information on practices that could assist states in improving their identification and successful pursuit of legally liable third party resources.