Inclusion Criteria:

• Ambulatory postmenopausal women based on medical history
• > or = 55 years of age at the start of screening
• Screening BMD values (g/cm²), at the lumbar spine OR femoral neck OR total hip that occur within the specified ranges based on the particular scanner that is used. At least 2 lumbar vertebrae must be evaluable by DXA, or at least one hip must be evaluable by DXA
• Provide written informed consent before any study specific procedure is performed.

Exclusion Criteria:

• Any disorder that compromises the ability of the subject to give written informed consent and/or to comply with study procedures
• Hyper- or hypothyroidism; however, stable subjects, in the investigator's opinion, on thyroid hormone replacement therapy are allowed
• Current hyper- or hypoparathyroidism
• Current hypo- or hyper calcemia based on the central laboratory reference ranges for albumin-adjusted serum calcium
• Rheumatoid arthritis, Paget's disease, Cushing's disease, hyperprolactinemia, or cirrhosis of the liver
• Any metabolic bone disease, e.g. osteomalacia or osteogenesis imperfecta, which may interfere with the interpretation of the findings
• Any symptomatic vertebral fracture within 3 months prior to screening
• Previous participation in clinical trials with denosumab
• Vitamin D deficiency [25(OH) vitamin D level < 20 ng/mL (<49.9nmol/L)]

• Contraindicated to alendronate therapy; contraindications for alendronate therapy include:

  1. Abnormalities of the esophagus, which delay esophageal emptying such as stricture or achalasia.
  2. Inability to stand or sit upright for at least 30 minutes.
  3. Hypersensitivity to ALN or other constituents of ALN tablets.
• Any known prior bisphosphonate use
• Currently enrolled in or has not yet completed at least 1 month since ending other investigational device or drug trail (s), or subject is receiving other investigational agent(s).