The "confrontation" referred to is the right guaranteed in the Sixth Amendment's Confrontation Clause. This guarantees that anyone charged with a crime be "confronted with the witnesses against him." While this may seem obvious in some situations, such as when someone is not physically present, things are not always so clear.
Although the Confrontation Clause has been around since the Bill of Rights was passed, a major shift in how it is applied occurred in 2004. In the case of Crawford v. Washington, the U.S. Supreme Court decided that "testimonial" statements are admissible only if the person who said them is unavailable and the accused had an earlier opportunity to cross-examine them (there is, of course, an exception where it can be shown that the accused caused the unavailability).
What is "testimonial"?
A problem arose from the fact that the Court did not define what "testimonial" means. The Court began to solve this in 2006 in Davis v. Washington. There, the Court ruled that a statement to 911 operators was not testimonial because it was made for the purpose of resolving an emergency, not as part of a police investigation.
This last point has become increasingly significant. In 2009, the Court ruled in Melendez-Diaz v. Massachusetts that certificates of analysis in a drug case were testimonial: they were created for the purpose of prosecution, and the analysts who created them knew this. In addition, the Court noted that they were functionally the same as in-court testimony. In a similar case, Bullcoming v. New Mexico, from 2011, the Court ruled for the same reason that an analyst other than the one who prepared a blood-alcohol report could not testify without violating the accused's right to confrontation.
Iowa v. Kennedy
One place where this comes up in Iowa law is the certified abstracts of someone's driving record. The Iowa Supreme Court recently considered whether the admission of these documents violated the Sixth Amendment in the case of Iowa v. Kennedy, and ultimately concluded that it did not. The records were a summary of information that the government held anyway, since the Iowa Department of Transportation maintains driving records for anyone with a license.
On the other hand, an affidavit of mailing, which demonstrates when the Department of Transportation mailed someone a notice of suspension, is testimonial. In the same case, the Iowa Supreme Court noted that these records were created for the sole purpose of showing that a specific defendant knew that his license had been revoked. Since they were created for the purposes of a criminal trial, they are testimonial for the purposes of the Sixth Amendment and thus the defendant had a right to confront the person who prepared them.
Effect of a violation of the Confrontation Clause
This does not mean that someone's sentence is automatically thrown out where the Confrontation Clause was violated. Instead, the court must decide whether that was a basis for the jury's decision. If the state can prove beyond a reasonable doubt that the violation had no effect on the verdict, then the sentence will be upheld in spite of the Sixth Amendment issue. This is evaluated on a case-by-case basis, and the court must try to determine how the jury reached the conclusion that it did.
As you can see, there are many layers to the constitutional rights we often take for granted. If you have been charged with a crime, it is important that you seek out qualified representation as soon as possible to ensure your rights are protected.