ChemGlobe: Thulium
- Electronic, thermal, and steric data along with an isotope table.
- http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/69.html

LANL: Thulium
- Basic information and history.
- http://periodic.lanl.gov/elements/69.html

Wikipedia: Thulium
- Properties of the element, including its history, applications, and characteristics.
- http://en.wikipedia.org/wiki/Thulium

Lenntech: Thulium
- Physical data, chemical properties, health and environmental effects.
- http://www.lenntech.com/Periodic-chart-elements/Tm-en.htm

EnvironmentalChemistry.com: Thulium
- Atomic structure, chemical and physical properties, and table of nuclides.
- http://environmentalchemistry.com/yogi/periodic/Tm.html

ChemicalElements.com: Thulium
- Basic information, atomic structure, and isotopes.
- http://www.chemicalelements.com/elements/tm.html

It's Elemental: Thulium
- Basic physical and historical information.
- http://education.jlab.org/itselemental/ele069.html

Visual Elements: Thulium
- Image, uses, physical information, and ionisation energies.
- http://www.chemsoc.org/viselements/pages/thulium.html