Some filename extensions—such as MOV, AVI, MXF, FLV, and F4V—denote container file formats rather than denoting a specific audio, video, or image data format. Container files can contain data encoded using various compression and encoding schemes. Premiere Pro can import these container files, but the ability to import the data that they contain is dependent on the codecs (specifically, decoders) installed.
By installing additional codecs, you can extend the ability of Premiere Pro to import additional file types. Many codecs installed into the operating system (Windows or Mac OS) work as a component inside the QuickTime or Video for Windows formats. Contact the manufacturer of your hardware or software for more information about codecs that work with the files that your specific devices or applications create. If Premiere Pro does not import your file, see this FAQ video tutorial, "Why can't Premiere Pro import my file?" for an explanation.
Video and still-image files that you want to import must not be more than the maximum dimensions allowed. For more information on maximum dimensions in Premiere Pro, see the Premiere Pro Work Area blog.
Adobe provides workflow guides for P2, RED, XDCAM, AVCCAM, and DSLR cameras and footage on the Adobe website.
Colin Brougham explains how Premiere Pro works natively with tapeless media (no transcoding) in this article and video series on the ProVideo Coalition website.
For more information about RED (R3D) digital cinema and Canon XF improvements in Premiere Pro CS5.5 and later, read this post on the Premiere Pro work area blog.
For an excellent explanation of importing files into Premiere Pro, see this excerpt from "An Editor's Guide to Premiere Pro," entitled, "Importing Media into Adobe Premiere Pro."