I)One is available on mobile only (Lightning Experience) and the other is only available on desktop (Salesforce Classic). II)The lightning bolt in the upper right corner (Lightning Experience) vs the cloud logo on the upper left (Salesforce Classic). III)Icons in the top right (Lightning Experience) vs the Force.com app menu in the top right (Salesforce Classic). IV)One makes you shockingly productive, while the other remains classically amazing. [bg_collapse view="button-orange" color="#4a4949" expand_text="Show Answers" collapse_text="Close Answer" ] III)Icons in the top right (Lightning Experience) vs the Force.com app menu in the top right (Salesforce Classic). [/bg_collapse]