Inclusion Criteria:

          -  Pathologically confirmed T or NK cell lymphoma at the enrolling institution. For CTCL,
             patients with stage IB disease or greater are eligible.

          -  Relapse or refractory disease after at least 1 systemic therapy except for T-PLL where
             untreated patients may be allowed after discussion with P.I.

          -  Age ≥ 18

          -  ECOG ≤ 2

          -  Measurable disease defined by:

               -  Lugano Classification for systemic lymphoma or

               -  Atypical and or malignant lymphocytes quantifiable by flow cytometry or
                  morphology in blood or bone marrow or

               -  mSWAT > 0 or Sezary count ≥ 1000 cells/μL for CTCL

          -  Previous systemic anti-cancer therapy for T-cell lymphoma must have been discontinued
             at least 2 weeks prior to treatment.

               -  Glucocorticoids aimed at controlling lymphoma-related symptoms are allowed as
                  long as they are tapered down to 20mg or less by the time of ruxolitiib
                  initiation

               -  Topical steroids for CTCL are permitted

               -  See section 6.2 Subject Exclusion Criteria for guideline regarding adjuvant and
                  maintenance therapy for prior malignancy

          -  Patients must meet the following lab criteria:

               -  ANC ≥ 1.0/mm^3 or ANC >/= 0.5/mm^3 (if patient has baseline neutropenia due to
                  lymphoma), platelets ≥ 100 x 10^9/L or ≥ 50 x 10^9/L (if related to lymphoma),
                  Hgb ≥ 8g/dL

               -  Patients with LGL or T-PLL are not required to meet a minimum ANC or hemoglobin
                  value for eligibility

               -  Total bilirubin ≤ 1.5 x upper limit of normal (ULN) or; ≤ 3 x ULN if documented
                  hepatic involvement with lymphoma, or ≤ 5 x ULN if history of Gilbert's ; AST and
                  ALT ≤ 3 x ULN; ≤ 5 x ULN if due to lymphoma involvement

               -  Creatinine clearance ≥ 30 mL/min; creatinine clearance of 15-29 mL/min will be
                  allowed as long as baseline platelets are ≥ 150 x 10^9/L

          -  For patients with positive hepatitis B core antibody or surface antigen, hepatitis B
             PCR must be negative and prophylaxis with entecavir or equivalent is required.

          -  Patients with HIV are allowed provided that they are on anti-retroviral treatment with
             no active infections.

        Exclusion Criteria:

          -  Any serious medical condition, laboratory abnormality, or psychiatric illness that
             would prevent the subject from signing the informed consent form.

          -  Uncontrolled concurrent illness including, but not limited to, ongoing or active
             infection, uncontrolled diabetes, clinically significant pneumonitis, symptomatic
             congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric
             illness/social situations that would limit compliance with study requirements.

          -  ECOG performance status >2

          -  Prior therapy with ruxolitinib

          -  Receiving systemic therapy for another primary malignancy (other than T-cell lymphoma)

               -  Patients with more than one type of lymphoma may be enrolled after discussion
                  with the MSK Principal Investigator

               -  Adjuvant or maintenance therapy to reduce the risk of recurrence of other
                  malignancy (other than T-cell lymphoma) is permissible after discussion with the
                  MSK principal Investigator

          -  Women of reproductive potential† must have a negative Serum ß human chorionic
             gonadotropin (ß-HCG) pregnancy test.

               -  A female of reproductive potential is a sexually mature female who: has not
                  undergone a hysterectomy or bilateral oophorectomy; or has not been naturally
                  postmenopausal for at least 24 consecutive months (i.e. has had menses at any
                  time in the preceding 24 consecutive months).