I write from the primary perspective of the Roman Catholic Lectionary. One of the fruits of the Second Vatican Council was work between Catholics and Protestants to develop a shared set of Sunday readings, which eventually came to be called the Revised Common Lectionary (RCL). You can read more about the history of the common lectionary on Wikipedia. Vanderbilt Divinity School has a wonderful resource site on the RCL which is my source for readings and terminology.
Although my website is geared towards covering the Catholic lectionary, I do include notes in the weekly email where the RCL diverges from that.