diff --git a/.circleci/config.yml b/.circleci/config.yml
index 0850393a..659513af 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -24,8 +24,8 @@ docs_deploy: &docs
 version: 2
 jobs:
   tests:
-    machine:
-      image: circleci/classic:201711-01
+    docker:
+      - image: circleci/python:3.7.6
     working_directory: /tmp/tests
     steps:
       - checkout:
@@ -33,9 +33,9 @@ jobs:
 
       - restore_cache:
           keys:
-            - deps-v6-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-{{ epoch }}
-            - deps-v6-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-
-            - deps-v6-
+            - deps-v8-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-{{ epoch }}
+            - deps-v8-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-
+            - deps-v8-
 
       - run:
           name: Get TemplateFlow Zip package
@@ -49,8 +49,8 @@ jobs:
       - run:
           name: Prepare environment
           command: |
-            pyenv global 3.5.2
-            virtualenv venv
+            python -m venv /tmp/venv
+            source /tmp/venv/bin/activate
             pip install -U pip
             pip install -r /tmp/src/templateflow/requirements.txt
             pip install "datalad ~= 0.11.8"
@@ -72,15 +72,16 @@ jobs:
             git config --global user.email "email@domain.com"
 
       - save_cache:
-          key: deps-v6-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-{{ epoch }}
+          key: deps-v8-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-{{ epoch }}
           paths:
-            - "/opt/circleci/.pyenv/versions/3.5.2"
             - "/tmp/data/templateflow"
             - "/tmp/cache"
+            - "/tmp/venv"
 
       - run:
           name: Update TemplateFlow skeleton
           command: |
+            source /tmp/venv/bin/activate
             datalad install -r -s  https://github.com/templateflow/templateflow $HOME/.cache/templateflow
             cd $HOME/.cache/templateflow/
             find . -type d -not -path "*/\.*" -exec mkdir -p /tmp/skel/{} \;
@@ -97,8 +98,7 @@ jobs:
       - run:
           name: Run tests (w/ DataLad)
           command: |
-            pyenv global 3.5.2
-            virtualenv venv
+            source /tmp/venv/bin/activate
             export TEMPLATEFLOW_USE_DATALAD=on
             pytest --junit-xml=/tmp/tests/datalad.xml --cov templateflow --cov-report xml:/tmp/cov_api_dl.xml \
                    --doctest-modules /tmp/src/templateflow/templateflow/api.py
@@ -106,18 +106,14 @@ jobs:
       - run:
           name: Submit api test coverage
           command: |
+            source /tmp/venv/bin/activate
             codecov --file /tmp/cov_api_dl.xml --root /tmp/src/templateflow \
                 --flags api,datalad -e CIRCLE_JOB
 
-
       - run:
           name: Run tests (pre-cached full TemplateFlow / no downloads)
-          environment:
-            TEMPLATEFLOW_USE_DATALAD: 0
-            TEMPLATEFLOW_HOME: "/tmp/data/templateflow"
           command: |
-            pyenv global 3.5.2
-            virtualenv venv
+            source /tmp/venv/bin/activate
             export TEMPLATEFLOW_HOME="/tmp/data/templateflow"
             pytest --junit-xml=/tmp/tests/wodatalad.xml --cov templateflow --cov-report xml:/tmp/cov_api_cached.xml \
                    --doctest-modules /tmp/src/templateflow/templateflow/api.py
@@ -125,14 +121,14 @@ jobs:
       - run:
           name: Submit api test coverage
           command: |
+            source /tmp/venv/bin/activate
             codecov --file /tmp/cov_api_cached.xml --root /tmp/src/templateflow \
                 --flags api,cached -e CIRCLE_JOB
 
       - run:
           name: Run tests (pulling from S3)
           command: |
-            pyenv global 3.5.2
-            virtualenv venv
+            source /tmp/venv/bin/activate
             export TEMPLATEFLOW_USE_DATALAD=off
             export TEMPLATEFLOW_HOME=$HOME/templateflow-s3
             pytest --junit-xml=/tmp/tests/s3.xml --cov templateflow --cov-report xml:/tmp/cov_api_s3.xml \
@@ -141,14 +137,14 @@ jobs:
       - run:
           name: Submit api test coverage
           command: |
+            source /tmp/venv/bin/activate
             codecov --file /tmp/cov_api_s3.xml --root /tmp/src/templateflow \
                 --flags api,s3 -e CIRCLE_JOB
 
       - run:
           name: Run tests (w/ DataLad, bypassed via S3)
           command: |
-            pyenv global 3.5.2
-            virtualenv venv
+            source /tmp/venv/bin/activate
             export TEMPLATEFLOW_USE_DATALAD=off
             export TEMPLATEFLOW_HOME=$HOME/templateflow-clean
             datalad install -r -s https://github.com/templateflow/templateflow $TEMPLATEFLOW_HOME
@@ -158,20 +154,21 @@ jobs:
       - run:
           name: Submit api test coverage
           command: |
+            source /tmp/venv/bin/activate
             codecov --file /tmp/cov_api_dl_s3.xml --root /tmp/src/templateflow \
                 --flags api,dls3 -e CIRCLE_JOB
 
       - run:
           name: Run tests (config, parameterized TEMPLATEFLOW_USE_DATALAD)
           command: |
-            pyenv global 3.5.2
-            virtualenv venv
+            source /tmp/venv/bin/activate
             pytest --junit-xml=/tmp/tests/conftests.xml --cov templateflow --cov-report xml:/tmp/cov_config.xml \
                    /tmp/src/templateflow/templateflow/conf/tests/test_conf.py
 
       - run:
           name: Submit config test coverage
           command: |
+            source /tmp/venv/bin/activate
             codecov --file /tmp/cov_config.xml --root /tmp/src/templateflow \
                 --flags config -e CIRCLE_JOB
 
@@ -181,8 +178,7 @@ jobs:
       - run:
           name: Test packaging
           command: |
-            pyenv global 3.5.2
-            virtualenv venv
+            source /tmp/venv/bin/activate
             cd /tmp/src/templateflow
             python setup.py sdist
             twine check dist/*
@@ -257,9 +253,9 @@ jobs:
 
       - restore_cache:
           keys:
-            - deps-v6-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-{{ epoch }}
-            - deps-v6-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-
-            - deps-v6-
+            - deps-v8-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-{{ epoch }}
+            - deps-v8-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-
+            - deps-v8-
 
       - add_ssh_keys:
           fingerprints:
@@ -300,8 +296,8 @@ jobs:
             git push origin HEAD:master
 
   deploy_pypi:
-    machine:
-      image: circleci/classic:201711-01
+    docker:
+      - image: circleci/python:3.7.6
     working_directory: /tmp/src/templateflow
     steps:
       - attach_workspace:
@@ -312,15 +308,14 @@ jobs:
 
       - restore_cache:
           keys:
-            - deps-v6-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-{{ epoch }}
-            - deps-v6-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-
-            - deps-v6-
+            - deps-v8-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-{{ epoch }}
+            - deps-v8-{{ checksum "/tmp/src/templateflow/requirements.txt"}}-
+            - deps-v8-
 
       - run:
           name: Deploy to PyPi
           command: |
-            pyenv global 3.5.2
-            virtualenv venv
+            source /tmp/venv/bin/activate
             pip install "setuptools>=27.0" twine
             python setup.py sdist
             twine check dist/*
diff --git a/.travis.yml b/.travis.yml
index 78de7e38..4948d50e 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -8,9 +8,9 @@ cache:
     - $HOME/.cache/pip
 
 python:
-  - 3.5
   - 3.6
   - 3.7
+  - 3.8
 
 env:
   global:
@@ -31,16 +31,16 @@ matrix:
   - python: 3.7
     env: CHECK_TYPE="style"
   allow_failures:
-  - python: 3.5
-    env: INSTALL_DEPENDS="pip==10.0.1 setuptools==30.3.0"
   - python: 3.6
     env: INSTALL_DEPENDS="pip==10.0.1 setuptools==30.3.0"
   - python: 3.7
     env: INSTALL_DEPENDS="pip==10.0.1 setuptools==30.3.0"
+  - python: 3.8
+    env: INSTALL_DEPENDS="pip==10.0.1 setuptools==30.3.0"
 
 before_install:
   - python -m pip install --upgrade $INSTALL_DEPENDS
-  - pip install "flake8<3.0" flake8-putty
+  - pip install -U flake8
 
 install:
   - |
@@ -59,7 +59,7 @@ install:
     fi
   - |
     if [ "$CHECK_TYPE" == "style" ]; then
-        travis_retry pip install "flake8<3.0" flake8-putty
+        travis_retry pip install -U flake8
     fi
 
 script:
diff --git a/setup.cfg b/setup.cfg
index 63d11b70..ba48f6fd 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -13,12 +13,12 @@ classifiers =
     Intended Audience :: Science/Research
     Topic :: Scientific/Engineering :: Image Recognition
     License :: OSI Approved :: Apache Software License
-    Programming Language :: Python :: 3.5
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
+    Programming Language :: Python :: 3.8
 
 [options]
-python_requires = >= 3.5
+python_requires = >= 3.6
 install_requires =
     pybids >= 0.9.2
     requests
@@ -76,3 +76,23 @@ versionfile_source = templateflow/_version.py
 versionfile_build = templateflow/_version.py
 tag_prefix =
 parentdir_prefix =
+
+[flake8]
+max-line-length = 99
+doctests = False
+exclude=*build/
+ignore =
+    W503
+
+[tool:pytest]
+norecursedirs = .git
+addopts = -svx
+doctest_optionflags = ALLOW_UNICODE NORMALIZE_WHITESPACE
+env =
+    PYTHONHASHSEED=0
+filterwarnings =
+    ignore::DeprecationWarning
+
+[coverage:run]
+branch = True
+
diff --git a/tox.ini b/tox.ini
deleted file mode 100644
index fc5dd07d..00000000
--- a/tox.ini
+++ /dev/null
@@ -1,16 +0,0 @@
-[flake8]
-max-line-length = 99
-doctests = False
-exclude=*build/
-
-[pytest]
-norecursedirs = .git
-addopts = -svx
-doctest_optionflags = ALLOW_UNICODE NORMALIZE_WHITESPACE
-env =
-    PYTHONHASHSEED=0
-filterwarnings =
-    ignore::DeprecationWarning
-
-[coverage:run]
-branch = True