Linagliptin Add-on to Insulin Background Therapy

Inclusion criteria: * Diagnosis of type 2 diabetes mellitus prior to informed consent. * Chinese male or female patients who are pre-treated with insulin alone or in combination with metformin: * With maximum insulin dose of \<= 1 unit/kg/day. Acceptable basal insulins could be insulin glargin, insulin detemir or NPH (neutral protamin hagedorn) insulin with duration of action up to 24 h; acceptable pre-mixed insulins could be preparations with 25/75 or 30/70 ratio, with once or twice daily posology only. The total insulin dose should not be changed by more than 10% of the baseline value within the 12 weeks prior to randomisation (Visit 3). Both human insulin \& insulin analogue are accepted. * If the patient is taking metformin, stable dose (at least 1500 mg daily) must be maintained for at least 12 weeks without dose adjustments prior to randomisation (Visit 3). * HbA1c fulfills the following criteria: \>= 7.5 % to \<= 10.0 % at Visit 1. * Age \>= 18 years at Visit 1. * BMI \<= 45 kg/m2 (Body Mass Index) at Visit 1. * Women of childbearing potential must be ready and able to use highly effective methods of birth control per ICH (International Conference on Harmonisation) M3 (R2) that result in a low failure rate of less than 1% per year when used consistently and correctly. A list of contraception methods meeting these criteria is provided in the patient information. * A woman is considered of childbearing potential (WOCBP), i.e. fertile, following menarche and until becoming post-menopausal unless permanently sterile. * Permanent sterilisation methods include hysterectomy, bilateral salpingectomy and bilateral oophorectomy. * Signed and dated written informed consent by date of Visit 1 in accordance with ICH-GCP (Good Clinical Practice) and local legislation Exclusion criteria: * Uncontrolled hyperglycaemic with a glucose level \>240 mg/dl (\>13.3 mmol/L) after an overnight fast during placebo run-in and confirmed by a second measurement (not on the same day). * Any other antidiabetic drug within 3 months prior to informed consent except those defined as background treatment via inclusion criterion 2. * Acute coronary syndrome (non-STEMI (ST Segment Elevation Myocardial Infarction), STEMI and unstable angina pectoris), stroke or TIA (Transient ischemic attack) within 3 months prior to informed consent. * Indication of liver disease, defined by serum levels of either ALT (Alanine aminotransferase) (SGPT (serum glutamic pyruvate transaminase )), AST (Aspartate aminotransferase) (SGOT (serum glutamic-oxaloacetic transaminase)), or alkaline phosphatase above 3 × upper limit of normal (ULN (upper limit of normal)) as determined during screening and/or run-in phase. * Any contraindications to metformin according to the local label for those patients that enter the study with metformin therapy as provided in ISF (Investigator Site File). * Bariatric surgery within the past two years and other gastrointestinal surgeries that induce chronic malabsorption. * Medical history of cancer (except for basal cell carcinoma) and/or treatment for cancer within the last 5 years. * Blood dyscrasias or any disorders causing hemolysis or unstable Red Blood Cell (e.g. malaria, babesiosis, haemolytic anemia). * Known hypersensitivity or allergy to the investigational product or its recipients. * Treatment with anti-obesity drugs 3 months prior to informed consent or any other treatment at the time of screening (i.e. surgery, aggressive diet regimen, etc.) leading to unstable body weight. * Current treatment with systemic steroids at time of informed consent or change in dosage of thyroid hormones within 6 weeks prior to informed consent or any other uncontrolled endocrine disorder except T2DM (Type 2 diabetes mellitus). * Women who are pregnant, nursing, or who plan to become pregnant while in the trial. * Alcohol or drug abuse within the 3 months prior to informed consent that would interfere with trial participation or any ongoing condition leading to a decreased compliance to study procedures or study drug intake in the opinion of the investigator. * Participation in another trial with an investigational drug within 2 months prior to informed consent or previous enrolment in this trial. * Any other clinical condition that would jeopardize patient's safety while participating in this clinical trial in the opinion of the investigator.