APA format requires that manuscripts include a "running head." Using a word processor, the running head is inserted into a document by inserting a header. Therefore, the terms running head and header are sometimes used interchangeably. The running head is simply the title of the document and the page number. It identifies the pages for the reader if pages get separated. Also, in journals that have multiple articles, the running head indicates the article title from a quick glance.
The running head contains the manuscript title, flushed to the left. However, a short title is used for titles more than 12 words or 50 characters (including spaces and punctuation). On the first page of a manuscript, the running head is preceded by the words "Running head" (in italics) and a colon. Subsequent pages only contain the title.
The header also contains the page number, flushed to the right. However, manuscripts conforming to APA format often include both roman and Arabic numerals. Per APA guidelines, roman numerals are used on introductory pages, such as pages of the document that contain an introduction, foreword, table of contents or dedication. Chapters, afterwords and subsequent pages use Arabic numerals. Sometimes, pages are counted but not numbered (e.g., title page, table of contents). Importantly, adjust the settings of the header to conform to specifications for the running head.
Normally, format the running head so that the characters reflect the same font used in the manuscript. The title should use all capital letters. Do not italicize or put it in quotes. Justify page numbers and flush them to the right for alignment. The header may overlap the page margins specified.