SCR is the prime catalyst of choice for NOx reduction in Diesel exhaust. Some years ago, there seemed to exist a window of chance for Lean NOx Trap (LNT), a competing technology, to capture part of the NOx reduction market. Research and development however increasingly demonstrated the superiority of urea-based SCR technology, first in regards to its higher overall efficiency in NOx reduction, second for its operation within a wider temperature range, third that, unlike LNT, it does not need any in-exhaust fuel injection resulting in fuel penalty. Fourth, SCR catalyst formulation is PGM-free, rendering a substantially lower catalyst cost. SCR is particularly more robust in lower exhaust temperature, a challenge in Diesel aftertreatment. Also, its higher overall NOx reduction efficiency allows for calibrating a higher engine-out NOx, resulting in improved fuel economy; this is non-trivial, since fuel costs (aka the total cost of ownership) play an important role in the commercial strategies for marketing vehicles, especially for long haul and other commercial vehicles (medium or heavy duty). It is therefore not surprising that a handful of medium and light duty Diesel vehicles equipped with LNT finally abandoned that strategy and nearly universally switched to SCR for their exhaust NOx reduction needs.