A Study to Evaluate the Safety and Efficacy of Denosumab and Ibandronate in Postmenopausal Women Sub-Optimally Treated With Daily or Weekly Bisphosphonates

Inclusion Criteria: * Ambulatory, postmenopausal women (based on medical history) 55 years or older at screening * Postmenopause will be defined as no vaginal bleeding or spotting for at least 12 months * If the subject is 55 - 59 years old and there is uncertainty regarding menopausal status, confirmation of serum FSH (\>= 50 mIU/mL) and serum estradiol (\<= 20 pg/mL) must be obtained * If the subject is 60 years or older, evaluation of FSH and estradiol levels is not needed to confirm menopausal status * Have received their first prescription of daily or weekly bisphosphonate therapy at least 1 month prior to screening * May have received * raloxifene, calcitonin, prior to initiation of daily orweekly bisphosphonate therapy. * up to 3 doses of monthly bisphosphonate prior to initiation of daily or weekly bisphosphonate therapy * calcium, and vitamin D * Hormone replacement therapy (e.g. estrogen use for mitigation of menopausal symptoms) * Subject has: * Stopped daily or weekly bisphosphonate therapy (is denoted as non-persistent) at least one month before the screening visit, or * Demonstrated low adherence to therapy assessed by a score of less than 6 on the OS-MMAS * Screening BMD (g/cm2) values, at the lumbar spine OR total hip, that occur within the following ranges, based on the particular scanner that is used: GE Lunar Lumbar spine 0.700 \< or = BMD \< and = 0.940 Total hip 0.504 \< or = BMD \< or = 0.756 Hologic Lumbar spine 0.607 \< or = BMD \< or = 0.827 Total hip 0.454 \< or = BMD \< or = 0.698 Both the initial and the repeat DXA scan of the lumbar spine OR the total hip must meet the above eligibility criteria. * At least 2 lumbar vertebrae must be evaluable by DXA. * At least one hip must be evaluable by DXA (eg, no history of either bilateral hip replacement or pins in both hips) * Provide signed informed consent before any study-specific procedures are conducted Exclusion Criteria: * Any disorder that compromises the ability of the subject to give written informed consent and/or to comply with study procedures * Current or prior use of medications prescribed for osteoporosis treatment other than oral daily or weekly bisphosphonate * Contraindicated to receive oral ibandronate 150mg PO QM, including * Hypersensitivity to ibandronate 150mg PO QM or other constituents of ibandronate 150mg PO QM tablets * Abnormalities of the esophagus, which delay esophageal emptying such as stricture or achalasia * Inability to stand or sit upright for at least 60 minutes * Administration of any of the following treatments within 3 months of screening * Tibolone * Anabolic steroids or testosterone * Glucocorticosteroids (\>= 5 mg prednisone equivalent per day for more than 10 days or a total cumulative dose of \>= 50 mg) * Vitamin D deficiency \[25(OH) vitamin D level \< 20 ng/mL (\<49.9 nmol/L)\] - Repletion will be allowed and subjects may be re-screened * Evidence of any of the following per subject report, chart review or central laboratory result: * Significantly impaired renal function as determined by estimated Glomerular Filtration Rate less that 30mL/min/1.73 m2 determined by the central laboratory * Current hypo- or hypercalcemia based on the central laboratory reference ranges * Active gastric or duodenal ulcer; or any history of significant gastrointestinal bleed requiring hospitalization or transfusion * Known to have tested positive for human immunodeficiency virus, hepatitis C virus, or hepatitis B surface antigen * Malignancy (except fully resected cutaneous basal cell or squamous cell carcinoma, cervical or breast ductal carcinoma in situ) within the last 5 years * Any metabolic bone disease or secondary cause of bone loss that is not controlled and may interfere with the interpretation of the findings * Previous participation in clinical trials with denosumab 60mg SC Q6M (regardless of treatment) * Received any solid organ or bone marrow transplant * Any laboratory abnormality which, in the opinion of the investigator, will prevent the subject from completing the study or interfere with the interpretation of the study results * Known sensitivity to mammalian cell derived drug products * Known intolerance to calcium supplements * Currently enrolled in or has not yet completed at least 1 month since ending other investigational device or drug trial(s) * Any physical or psychiatric disorder which, in the opinion of the investigator, will prevent the subject from completing the study or interfere with the interpretation of the study results * Evidence of alcohol or substance-abuse within the last 12 months which the investigator believes would interfere with understanding or completing the study