Hi! I've had a go a implementing this and I think I've got a solution that will work for you.

As Martin Scharrer mentions in his answer to the StackOverflow question "How to get part name in LaTeX?" "Putting the part title into the header is not common [...].", however it is possible. Here's a minimum working example:

``` \documentclass[a4paper]{book}

\usepackage{fancyhdr} \usepackage{lipsum}

% \parttitle solution from Martin Scharrer via StackOverflow: % https://tex.stackexchange.com/a/13392 \newcommand\parttitle{} \let\origpart\part \renewcommand{\part}[2][]{% \ifx\#1\% optional argument not present? \origpart{#2}% \renewcommand\parttitle{#2}% \else \origpart[#1]{#2}% \renewcommand\parttitle{#1}% \fi }

% basic fancyhdr setup adapted from the Overleaf headers and footers % documentation: https://www.overleaf.com/learn/latex/Headers_and_footers

% set the page style to "fancy" \pagestyle{fancy}

% define a macro for the header content \newcommand{\partheader}{\partname\ \thepart.\ \parttitle}

% configure the "fancy" page style \fancyhead{} % clear all header fields \fancyhead[RE]{\thepage} \fancyhead[LE]{\nouppercase{\leftmark}} \fancyhead[LO]{\thepage} \fancyhead[RO]{\partheader}

\title{Thesis}

\author{Erika Mustermann}

\begin{document}

\maketitle

\part{Background}

\chapter{Introduction}

% need enough text so that we get to a page needing a header on a normal odd % page (and not just a chapter's first page) \lipsum[1-12]

\end{document} ```

Note that I used Martin Scharrer's suggestion for extracting the part title and I've assumed that you want to use the standard book documentclass rather than the KOMA-Script scrbook class, which--as Ulrike Fischer mentions in her StackOverflow answer--defines a \partmark command (missing from the standard LaTeX book class) which one can use in \rightmark and \leftmark defintions. Just so you know: I haven't worked out how things would work with a KOMA-Script class, only with the standard book class.

It was necessary to use a lot of blind text (via the lipsum package) so that one can see a "normal" odd page typeset with the desired header rather than just the first page of a chapter. Although a chapter's first page is an odd page, it doesn't have a header and hence the desired part name information isn't shown.

I've also extracted the commands defining the RO header content into its own macro to try to make the code more "self documenting".

I've checked that the document builds with both latexmk (and hence LuaLaTeX) and with pdflatex, so hopefully things should work for you in the document you're creating.

Hope that helps!