Inclusion Criteria:

   - Histologic proof of Grade 1, 2, or 3a follicular lymphoma (FL) without clinical or
   pathological evidence of transformation

   - Previously treated with at least 2 prior lines of therapy, including at least 1
   rituximab combination chemotherapy regimen; last prior line of therapy includes an
   anti CD20 monoclonal antibody-containing chemotherapy regimen (separate lines of
   therapy are defined as different regimens that are either separated by disease
   progression, refractory disease, or relapsed disease)

   - Resistant disease to the last therapy, defined as progression of disease during or
   within 12 months of the last dose of chemotherapy in a CD20 antibody combination
   chemotherapy regimen

   - At least 1 measurable site of disease according to International Working Group Revised
   Response Criteria for Malignant Lymphoma

   - Eastern Cooperative Oncology Group performance status grade 0 or 1

   - Hematology and biochemical laboratory values must be within protocol-defined
   parameters within 7 days prior to enrollment

   - Agrees to protocol-defined use of effective contraception

   - Women of childbearing potential must have a negative serum or urine pregnancy test at
   screening

Exclusion Criteria:

   - Prior nitrosoureas within 6 weeks, chemotherapy within 3 weeks, therapeutic anticancer
   antibodies within 4 weeks, radio- or toxin-immunoconjugates within 10 weeks, radiation
   therapy or other investigational agents within 3 weeks, or major surgery within 4
   weeks of first dose of study drug

   - Prior treatment with PCI-32765 or other Bruton's tyrosine kinase inhibitors (patients
   who progressed or became refractory while on treatment with PI3K inhibitors are
   excluded)

   - Concurrent enrollment in another therapeutic investigational clinical treatment study

   - Received a prior allogeneic hematopoietic stem cell transplant (prior autologous
   hematopoietic stem cell transplant is allowed)

   - Known central nervous system lymphoma

   - History of prior malignancy (except malignancy treated with curative intent and with
   no known active disease present for >=3 years before enrollment, adequately treated
   non-melanoma skin cancer or lentigo maligna without evidence of disease, or adequately
   treated cervical carcinoma in situ without evidence of disease)

   - History of stroke or intracranial hemorrhage within 6 months prior to enrollment

   - Requires anticoagulation with warfarin or equivalent vitamin K antagonists

   - Requires treatment with strong cytochrome P450 (CYP)3A4/5 inhibitors

   - Clinically significant cardiovascular disease such as uncontrolled or symptomatic
   arrhythmias, congestive heart failure, or myocardial infarction within 6 months of
   screening, or any Class 3 (moderate) or Class 4 (severe) cardiac disease as defined by
   the New York Heart Association Functional Classification

   - Known history of Human Immunodeficiency Virus (HIV) or active infection with Hepatitis
   C or active infection with Hepatitis B or any uncontrolled active systemic infection
   requiring intravenous antibiotics

   - Women who are pregnant or breastfeeding

   - Any life-threatening illness, medical condition, or organ system dysfunction which, in
   the investigator's opinion, could compromise the patient's safety, interfere with the
   absorption or metabolism of PCI-32765 capsules, or put the study outcomes at undue
   risk