The recent New Jersey Supreme Court decision in State v. Brown provides a primer on the Constitution's seemingly straightforward ex post facto clause and an enlightening discussion showing how it is not always so simple to apply. The Brown case raised the interesting and close question of whether it is legal under the New Jersey and federal constitutions to sentence a sex offender for failure to register under a statute that increased the failure-to-register offense from a fourth-degree offense to a third-degree offense after the original crime was committed but before the failure to register (a Megan's Law requirement) occurred. In other words, as analyzed by Brown's 6-1 majority, the question posed is: was the failure to register part of the original sex offense—in which case the ex post facto clause would bar the more recently enacted increased penalty—or was it an entirely new and separate crime occurring after the increased penalty was enacted?