Write-up for a NIT Calicut school in March 2021. It treats radiative transfer in the solar atmosphere in complexity order of non-local control in space, wavelength, time and uses classic literature for illustration. It adds many yellow-page endnotes detailing specific cases. On-screen reading with web acess is a must because it contains many page-opening hyperlinks to my on-line materials and to public literature. It may be read cursorily for a quick overview but it becomes a comprehensive course when studying all notes and links, the latter serving as convenient pointers and page openers. These are also useful for researchers selecting a topic suiting their interest.