Lowering low-density lipoprotein cholesterol (LDL-C) is a wellestablished strategy for cardiovascular risk reduction. Inherently, the focus is on LDL’s cholesterol content rather than its particle concentration. However, a number of studies have demonstrated that measures of particles burden, such as apolipoprotein B (apoB) and LDL particle concentration (LDL-P) can be discordant with LDL-C. When discordant, they appear to more strongly predict cardiovascular events, compared with LDL-C. Triglyceride-rich lipoproteins (TRL) play a key role in generating small dense LDL particles and are now causally implicated in atherosclerosis. This book chapter reviews the most important information about TRL, apoB, and LDL-P, and discusses relevant scenarios for the clinician where discordance between lipoprotein cholesterol content and lipoprotein particle concentration measurements should be considered.