diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..86909ae
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,3 @@
+[build-system]
+requires = ["setuptools>=43", "wheel"]
+build-backend = "setuptools.build_meta"
\ No newline at end of file
diff --git a/requirements.txt b/requirements.txt
deleted file mode 100644
index b539925..0000000
--- a/requirements.txt
+++ /dev/null
@@ -1 +0,0 @@
-pyparsing==2.4.6
diff --git a/pyvalem/__init__.py b/scr/pyvalem/__init__.py
similarity index 100%
rename from pyvalem/__init__.py
rename to scr/pyvalem/__init__.py
diff --git a/pyvalem/atom_data.py b/scr/pyvalem/atom_data.py
similarity index 100%
rename from pyvalem/atom_data.py
rename to scr/pyvalem/atom_data.py
diff --git a/pyvalem/atomic_configuration.py b/scr/pyvalem/atomic_configuration.py
similarity index 100%
rename from pyvalem/atomic_configuration.py
rename to scr/pyvalem/atomic_configuration.py
diff --git a/pyvalem/atomic_term_symbol.py b/scr/pyvalem/atomic_term_symbol.py
similarity index 100%
rename from pyvalem/atomic_term_symbol.py
rename to scr/pyvalem/atomic_term_symbol.py
diff --git a/pyvalem/atomic_weights.txt b/scr/pyvalem/atomic_weights.txt
similarity index 100%
rename from pyvalem/atomic_weights.txt
rename to scr/pyvalem/atomic_weights.txt
diff --git a/pyvalem/diatomic_molecular_configuration.py b/scr/pyvalem/diatomic_molecular_configuration.py
similarity index 100%
rename from pyvalem/diatomic_molecular_configuration.py
rename to scr/pyvalem/diatomic_molecular_configuration.py
diff --git a/pyvalem/formula.py b/scr/pyvalem/formula.py
similarity index 100%
rename from pyvalem/formula.py
rename to scr/pyvalem/formula.py
diff --git a/pyvalem/generic_excited_state.py b/scr/pyvalem/generic_excited_state.py
similarity index 100%
rename from pyvalem/generic_excited_state.py
rename to scr/pyvalem/generic_excited_state.py
diff --git a/pyvalem/isotope_masses.txt b/scr/pyvalem/isotope_masses.txt
similarity index 100%
rename from pyvalem/isotope_masses.txt
rename to scr/pyvalem/isotope_masses.txt
diff --git a/pyvalem/key_value_pair.py b/scr/pyvalem/key_value_pair.py
similarity index 100%
rename from pyvalem/key_value_pair.py
rename to scr/pyvalem/key_value_pair.py
diff --git a/pyvalem/molecular_term_symbol.py b/scr/pyvalem/molecular_term_symbol.py
similarity index 100%
rename from pyvalem/molecular_term_symbol.py
rename to scr/pyvalem/molecular_term_symbol.py
diff --git a/pyvalem/racah_symbol.py b/scr/pyvalem/racah_symbol.py
similarity index 100%
rename from pyvalem/racah_symbol.py
rename to scr/pyvalem/racah_symbol.py
diff --git a/pyvalem/reaction.py b/scr/pyvalem/reaction.py
similarity index 100%
rename from pyvalem/reaction.py
rename to scr/pyvalem/reaction.py
diff --git a/pyvalem/rotational_state.py b/scr/pyvalem/rotational_state.py
similarity index 100%
rename from pyvalem/rotational_state.py
rename to scr/pyvalem/rotational_state.py
diff --git a/pyvalem/special_cases.py b/scr/pyvalem/special_cases.py
similarity index 100%
rename from pyvalem/special_cases.py
rename to scr/pyvalem/special_cases.py
diff --git a/pyvalem/state.py b/scr/pyvalem/state.py
similarity index 100%
rename from pyvalem/state.py
rename to scr/pyvalem/state.py
diff --git a/pyvalem/state_parser.py b/scr/pyvalem/state_parser.py
similarity index 100%
rename from pyvalem/state_parser.py
rename to scr/pyvalem/state_parser.py
diff --git a/pyvalem/stateful_species.py b/scr/pyvalem/stateful_species.py
similarity index 100%
rename from pyvalem/stateful_species.py
rename to scr/pyvalem/stateful_species.py
diff --git a/pyvalem/utils.py b/scr/pyvalem/utils.py
similarity index 100%
rename from pyvalem/utils.py
rename to scr/pyvalem/utils.py
diff --git a/pyvalem/vibrational_state.py b/scr/pyvalem/vibrational_state.py
similarity index 100%
rename from pyvalem/vibrational_state.py
rename to scr/pyvalem/vibrational_state.py
diff --git a/setup.cfg b/setup.cfg
new file mode 100644
index 0000000..41cf804
--- /dev/null
+++ b/setup.cfg
@@ -0,0 +1,3 @@
+[metadata]
+# This includes the license file(s) in the wheel (requires setuptools>=42)
+license_files = LICENSE
\ No newline at end of file
diff --git a/setup.py b/setup.py
index d440d97..12c06f4 100644
--- a/setup.py
+++ b/setup.py
@@ -1,36 +1,51 @@
-import os
 from setuptools import setup, find_packages
+from pathlib import Path
 
-long_description = """PyValem is a Python package for parsing, validating, manipulating and interpreting the chemical formulas, quantum states and labels of atoms, ions and small molecules.
+root = Path(__file__).parent.resolve()
 
-Species and states are specfied as strings using a simple and flexible syntax, and may be compared, output in different formats and manipulated using a variety of predefined Python methods.
-
-See https://github.com/xnx/pyvalem for documentation and more information.
-"""
-
-# Read in dependencies list from requirements.txt
-thelibFolder = os.path.dirname(os.path.realpath(__file__))
-requirementPath = thelibFolder + '/requirements.txt'
-install_requires = []
-if os.path.isfile(requirementPath):
-    with open(requirementPath) as f:
-        install_requires = f.read().splitlines()
+# Get the long description from the README file
+long_description = (root / "README.rst").read_text(encoding="utf-8")
 
 setup(
-    name = 'pyvalem',
-    version = '2.3.0',
-    author = 'Christian Hill, Martin Hanicinec',
-    author_email = 'ch.hill@iaea.org',
-    description = 'A package for managing simple chemical species and states',
+    name='pyvalem',
+    version='2.4.0',
+    description='A package for managing simple chemical species and states',
     long_description=long_description,
-    long_description_content_type="text/markdown",
-    url = 'https://github.com/xnx/pyvalem',
-    packages = find_packages(),
-    install_requires=install_requires,
+    long_description_content_type="text/x-rst",
+    url='https://github.com/xnx/pyvalem',
+    author='Christian Hill',
+    author_email='ch.hill@iaea.org',
     classifiers=[
-        "Programming Language :: Python :: 3",
+        "Development Status :: 4 - Beta",
+        "Intended Audience :: Science/Research",
+        "Topic :: Scientific/Engineering :: Chemistry",
+        "Topic :: Scientific/Engineering :: Physics",
         "License :: OSI Approved :: GNU General Public License v3 (GPLv3)",
+        "Programming Language :: Python :: 3",
+        "Programming Language :: Python :: 3.4",
+        "Programming Language :: Python :: 3.5",
+        "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
+        "Programming Language :: Python :: 3.11",
+        "Programming Language :: Python :: 3 :: Only",
+        "Operating System :: OS Independent",
     ],
+    keywords="chemistry, formula, species, state, reaction",
+    package_dir={'': 'src'},
+    packages=find_packages(where='src'),
     python_requires='>=3.4',
+    install_requires=[
+        "pyparsing",
+        'importlib-resources; python_version < "3.7.0"'
+    ],
+    extras_require={
+        'dev': ["check-manifest", "black", "coverage", "pytest", "ipython"]
+    },
     package_data={'pyvalem': ['atomic_weights.txt', 'isotope_masses.txt']},
+    project_urls={
+        "Bug Reports": "https://github.com/xnx/pyvalem/issues",
+    },
 )
diff --git a/test/__init__.py b/test/__init__.py
deleted file mode 100644
index e69de29..0000000