Two systems
The United States has two court systems running side by side. Each state has its own courts, with its own constitution, statutes, rules and jury instructions. The federal courts sit in every state as well. They have one Constitution and one set of federal statutes and rules, and jury instructions that differ by region. A person in any state can be tried in either system, depending on the charge.
That is why this guide has fifty-two chapters and not fifty: the fifty states, the District of Columbia, and the federal courts as a jurisdiction of their own.
Which court, which law
Most criminal trials in the country happen in state courts, under state law. Federal courts try federal charges. The rules on jurors follow the court, not the person: a juror in a state court is governed by that state's law on selection, instructions, verdicts and protections, and a juror in a federal court by federal law, wherever the courthouse stands.
The two systems answer this guide's questions differently. Each state writes its own standard instruction, or none. The federal courts have their own, and it is not the same in every part of the country. The size of a jury and the agreement it needs are set separately in each system too.
Where they meet
The two systems are not sealed off from each other. The federal Constitution sets a floor that every state court has to respect, and the state constitutions often add to it. A rule that applies in a state court may have come from a federal decision, or may go further than one. The chapters note where a state's rule rests on federal ground and where it stands on the state's own text.
Your state, and the federal courts in it
For a reader, the practical question is which chapter to open. A summons from a county or state court means the state's chapter. A summons from a United States District Court means the federal chapter, and that chapter also explains how the federal instructions vary from one region of the country to another. Both chapters are built on the same six parts, so the two can be read side by side.