ChemGlobe: Hafnium
- Electronic, thermal, and steric data along with an isotope table.
- http://partisans.spurious.biz/~pkremer/projects/chemglobe/ptoe/_/72.html

LANL: Hafnium
- History, properties, uses, and handling.
- http://periodic.lanl.gov/elements/72.html

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

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

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

Visual Elements: Hafnium
- General and physical information, source, uses, key isotopes, and ionisation energies.
- http://www.chemsoc.org/viselements/pages/hafnium.html

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

It's Elemental: Hafnium
- Basic physical and historical information.
- http://education.jlab.org/itselemental/ele072.html

Britannica Nobel Prize: Hafnium
- Detailed overview and data.
- http://www.britannica.com/nobel/micro/254_6.html