经外书类似次经，不过所指略为不同。经外书泛指基督教或新教教徒认定；天主教所属圣经与基督教圣经中差异的部分多余经文。经外书产生的主因，在于1611年詹姆士王道版圣经后，基督新教教会陆续将部份经文自圣经中删除，用意为大众提供比较短小、经济的圣经版本。至此，多数基督新教信徒认为此部分遭删除经文属天主教，并称为经外书。

经外书最广为人知的为《死海手卷》、《所罗门的智能》与《萨拉克的智能》，这部分经外书含有大量谚语和智能格言的书，而经外书所呈现的宗教为一个更加超自然的宗教，是一个强调体验天国或灵性境界的宗教。

The Biblical apocrypha (from the Greek ἀπόκρυφος, apókruphos, meaning "hidden") denotes the collection of ancient books found, in some editions of the Bible, in a separate section between the Old and New Testaments or as an appendix after the New Testament. Although the term apocrypha had been in use since the 5th century, it was in Luther's Bible of 1534 that the Apocrypha was first published as a separate intertestamental section. To this date, the Apocrypha is "included in the lectionaries of Anglican and Lutheran Churches." Moreover, the Revised Common Lectionary, in use by most mainline Protestants including Methodists and Moravians, lists readings from the Apocrypha in the liturgical kalendar, although alternate Old Testament scripture lessons are provided.