diff --git a/src/TopDownProteomics/ProForma/TopPicProformaParser.cs b/src/TopDownProteomics/ProForma/TopPicProformaParser.cs
new file mode 100644
index 0000000..9877e34
--- /dev/null
+++ b/src/TopDownProteomics/ProForma/TopPicProformaParser.cs
@@ -0,0 +1,216 @@
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text.RegularExpressions;
+
+namespace TopDownProteomics.ProForma;
+
+/// <summary>
+/// A parser for TopPIC strings into a ProformaTerm <see cref="ProFormaTerm"/>
+/// </summary>
+public class TopPicProformaParser
+{
+    IDictionary<string, IList<ProFormaDescriptor>>? _modLookup = null;
+
+    #region Regex strings
+    Regex _modRx = new(@"\(([A-Z]{1,})\)(\[.+?\])+");
+    Regex _numberRx = new(@"(-?\+?[0-9]+.[0-9]+)");
+    Regex _terminalAaRx = new(@"\P{N}(\.)\P{N}??|\P{N}??(\.)\P{N}");
+    Regex _strippedSequenceRx = new(@"\[.+?\]|[()]");
+    #endregion
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TopPicProformaParser"/> class.
+    /// </summary>
+    public TopPicProformaParser() { }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TopPicProformaParser"/> class.
+    /// </summary>
+    /// <param name="modFile">The mod.txt file for mapping modifications.</param>
+    public TopPicProformaParser(string modFile)
+    {
+        _modLookup = ParseModFile(new FileInfo(modFile).OpenRead()); ;
+    }
+
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TopPicProformaParser"/> class.
+    /// </summary>
+    /// <param name="modStream">The mod stream.</param>
+    public TopPicProformaParser(Stream modStream)
+    {
+        _modLookup = ParseModFile(modStream);
+    }
+
+    /// <summary>
+    /// Gets the proforma term.
+    /// </summary>
+    /// <param name="sequence">The sequence.</param>
+    /// <returns></returns>
+    public ProFormaTerm ParseTopPicString(string sequence)
+    {
+        //first remove terminal AA tags if there!
+        sequence = RemoveTerminalAAs(sequence);
+        var (nTerms, cTerms, tags) = FindPTMs(sequence);
+        return new ProFormaTerm(GetFullyStrippedSequence(sequence), tags, nTerms, cTerms);
+    }
+
+    private IDictionary<string, IList<ProFormaDescriptor>> ParseModFile(Stream modStream)
+    {
+        IDictionary<string, IList<ProFormaDescriptor>> modLookup = new Dictionary<string, IList<ProFormaDescriptor>>();
+
+        using StreamReader reader = new StreamReader(modStream);
+
+        while (!reader.EndOfStream)
+        {
+            var line = reader.ReadLine();
+
+            if (string.IsNullOrWhiteSpace(line) | line.StartsWith("#"))
+                continue;
+
+            //# To input a modification, use the following format:
+            //# Name,Mass,Residues,Position,UnimodID
+            var splitLine = line.Split(',');
+
+            if (splitLine.Length != 5)
+                throw new TopPicParserException("Failed to parse mod file");
+
+            var name = splitLine[0];
+
+            if (int.TryParse(splitLine[4], out var uniModNumber))
+            {
+                if (uniModNumber > 0)
+                    modLookup.Add(name, new List<ProFormaDescriptor>()
+                    {
+                        new ProFormaDescriptor(ProFormaKey.Identifier, ProFormaEvidenceType.Unimod, $"UNIMOD:{uniModNumber}"),
+                        new ProFormaDescriptor(ProFormaKey.Info, name)
+                    });
+                else if (uniModNumber == -1 && double.TryParse(splitLine[1], out var mass))
+                    modLookup.Add(name, new List<ProFormaDescriptor>()
+                    {
+                        new ProFormaDescriptor(ProFormaKey.Mass, $"{mass:+#.000000;-#.000000}"),
+                        new ProFormaDescriptor(ProFormaKey.Info, name)
+                    });
+                else
+                    throw new TopPicParserException($"invalid UniMod Id or mass");
+            }
+            else
+                throw new TopPicParserException($"Failed to parse UniMod Id {splitLine[4]}".Trim());
+        }
+        return modLookup;
+    }
+
+    private string GetFullyStrippedSequence(string sequence) => _strippedSequenceRx.Replace(sequence, "");
+
+    private Dictionary<int, int> GetIndexLookup(string sequence)
+    {
+        Dictionary<int, int> indexLookup = new Dictionary<int, int>();
+
+        bool inBracket = false;
+        int index = 0;
+        for (int i = 0; i < sequence.Length; i++)
+        {
+            char c = sequence[i];
+            if (c == '[')
+                inBracket = true;
+            else if (c == ']')
+                inBracket = false;
+            else if (char.IsUpper(c) && !inBracket)
+            {
+                indexLookup[i] = index++;
+            }
+        }
+        return indexLookup;
+    }
+
+    private Tuple<IList<ProFormaDescriptor>, IList<ProFormaDescriptor>, IList<ProFormaTag>> FindPTMs(string sequence)
+    {
+        var indexLookup = GetIndexLookup(sequence);
+
+        List<ProFormaDescriptor> nTerms = new List<ProFormaDescriptor>();
+        List<ProFormaDescriptor> cTerms = new List<ProFormaDescriptor>();
+        List<ProFormaTag> tags = new List<ProFormaTag>();
+
+        foreach (Match match in _modRx.Matches(sequence))
+        {
+            var startIndex = indexLookup[match.Groups[1].Index];
+            var ptms = match.Groups[2].Captures;
+
+            if (ptms.Count > 1)
+                throw new TopPicParserException("multiple mods are not currently supported");
+
+            if (startIndex == 0 && match.Groups[1].Length == 1)  // check for ambiguous mods that include the start -> just make tags
+            {
+                nTerms = ParsePtms(ptms);
+            }
+            else if (startIndex == indexLookup.Max(x => x.Value))
+            {
+                cTerms = ParsePtms(ptms);
+            }
+            else if (match.Groups[1].Length > 1)
+            {
+                var EndIndex = startIndex + match.Groups[1].Length - 1;
+                tags.Add(new ProFormaTag(startIndex, EndIndex, ParsePtms(ptms)));
+            }
+            else
+                tags.Add(new ProFormaTag(startIndex, ParsePtms(ptms)));
+        }
+        return new Tuple<IList<ProFormaDescriptor>, IList<ProFormaDescriptor>, IList<ProFormaTag>>(nTerms, cTerms, tags);
+    }
+
+    private List<ProFormaDescriptor> ParsePtms(CaptureCollection ptms)
+    {
+        var proformaList = new List<ProFormaDescriptor>();
+
+        foreach (var ptm in ptms)
+            proformaList.AddRange(ParsePtmString(ptm.ToString()));
+
+        return proformaList;
+    }
+
+    private IList<ProFormaDescriptor> ParsePtmString(string ptmString)
+    {
+        //strip []
+        ptmString = ptmString.Substring(1, ptmString.Length - 2);
+        var numberMatch = _numberRx.Match(ptmString);
+
+        if (numberMatch.Success && Double.TryParse(numberMatch.Value, out double val))
+            return new List<ProFormaDescriptor>() { new ProFormaDescriptor(ProFormaKey.Mass, $"{val:+#.0000;-#.0000;0}")};
+        
+        // Find and throw exception if there is a *
+        if (ptmString.Contains('*'))
+            throw new TopPicParserException("multiple mods are not currently supported");
+
+        if (_modLookup?.ContainsKey(ptmString) == true)
+            return _modLookup[ptmString];
+        else
+            return new List<ProFormaDescriptor>() { new ProFormaDescriptor(ptmString) };
+    }
+
+    private string RemoveTerminalAAs(string sequence)
+    {
+        var matches = _terminalAaRx.Matches(sequence);
+
+        if (matches.Count > 0)
+        {
+            var startIndex = matches[0].Groups[1].Index + 1;
+            var length = matches[1].Groups[1].Index - startIndex;
+            sequence = sequence.Substring(startIndex, length);
+        }
+        return sequence;
+    }
+}
+
+/// <summary>
+/// An exception for the TopPIC to ProForma parser.
+/// </summary>
+/// <seealso cref="System.Exception" />
+public class TopPicParserException : Exception
+{
+    /// <summary>
+    /// Initializes a new instance of the <see cref="TopPicParserException"/> class.
+    /// </summary>
+    /// <param name="message">The message that describes the error.</param>
+    public TopPicParserException(string message) : base(message) { }
+}
\ No newline at end of file
diff --git a/tests/TopDownProteomics.Tests/ProForma/ToPicParserTests.cs b/tests/TopDownProteomics.Tests/ProForma/ToPicParserTests.cs
new file mode 100644
index 0000000..787c312
--- /dev/null
+++ b/tests/TopDownProteomics.Tests/ProForma/ToPicParserTests.cs
@@ -0,0 +1,100 @@
+using NUnit.Framework;
+using System.IO;
+using System.Text;
+using TopDownProteomics.ProForma;
+
+namespace TopDownProteomics.Tests.ProForma;
+
+/// <summary>
+/// Tests for the TopPicProformaParser <see cref="TopPicProformaParser"/>
+/// </summary>
+[TestFixture]
+public class ToPicParserTests
+{
+    private static string GetTestDataFile(string name) => Path.Combine(TestContext.CurrentContext.TestDirectory, "TestData", name);
+
+    /// <summary>
+    /// Tests the TopPic Proforma Parser.
+    /// </summary>
+    [Test]
+    [TestCase("M.A(AAA)[Phospho]AAA.C", "A(AAA)[UNIMOD:21|Info:Phospho]AAA")]
+    [TestCase("W.(G)[Oxidation]DGCAQKNKPGVYTK(V)[Phospho]YNYVKWIKNTIAANS.", "[UNIMOD:35|Info:Oxidation]-GDGCAQKNKPGVYTKV[UNIMOD:21|Info:Phospho]YNYVKWIKNTIAANS")]
+    [TestCase(".GDGCAQKNKPGVYTK(V)[Phospho]YNYVKWIKNTIAANS.", "GDGCAQKNKPGVYTKV[UNIMOD:21|Info:Phospho]YNYVKWIKNTIAANS")]
+    [TestCase("W.GDGCAQKNKPGVYTKVYNYVKWIKNTIAAN(S)[Phospho].", "GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS-[UNIMOD:21|Info:Phospho]")]
+    [TestCase("W.GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS.", "GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS")]
+    [TestCase(".(G)[Test1]DGCAQKNKPGVYTKVYNYVKWIKNTIAANS.", "[+59.000000|Info:Test1]-GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS")]
+    [TestCase("W.(G)[T@s!1]DGCAQKNKPGVYTKVYNYVKWIKNTIAANS.", "[T@s!1]-GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS")]
+    [TestCase("W.(G)[Test_2]DGCAQKNKPGVYTKVYNYVKWIKNTIAANS.", "[+59.000000|Info:Test_2]-GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS")]
+    [TestCase(".(G)[Ox_plus1]DGCAQKNKPGVYTKVYNYVKWIKNTIAANS.", "[+17.123000|Info:Ox_plus1]-GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS")]
+    [TestCase(".(G)[+23.9987]DGCAQKNKPGVYTKVYNYVKWIKNTIAANS.", "[+23.9987]-GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS")]
+    [TestCase(".(G)[23.9987]DGCAQKNKPGVYTKVYNYVKWIKNTIAANS.", "[+23.9987]-GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS")]
+    [TestCase(".(G)[-23.9987]DGCAQKNKPGVYTKVYNYVKWIKNTIAANS.", "[-23.9987]-GDGCAQKNKPGVYTKVYNYVKWIKNTIAANS")]
+    public void CompareToProForma(string topPIC, string proForma)
+    {
+        var topicParser = new TopPicProformaParser(GetTestDataFile("topPicTestMods.txt"));
+        var term = topicParser.ParseTopPicString(topPIC);
+
+        var writer = new ProFormaWriter();
+
+        Assert.AreEqual(proForma, writer.WriteString(term));
+    }
+
+    /// <summary>
+    /// Tests the TopPic Proforma Parser with no mod file.
+    /// </summary>
+    [Test]
+    [TestCase("M.A(AAA)[Phospho]AAA.C", "A(AAA)[Phospho]AAA")]
+    [TestCase("W.(G)[Oxidation]DGCAQKNKPGVYTK(V)[Phospho]YNYVKWIKNTIAANS.", "[Oxidation]-GDGCAQKNKPGVYTKV[Phospho]YNYVKWIKNTIAANS")]
+    [TestCase("W.(G)[asdf4fdfsd6!]DGCAQKNKPGVYTKYNYVKWIKNTIAANS.", "[asdf4fdfsd6!]-GDGCAQKNKPGVYTKYNYVKWIKNTIAANS")]
+    public void CompareToProFormaNoModFile(string topPIC, string proForma)
+    {
+        var topicParser = new TopPicProformaParser();
+        var term = topicParser.ParseTopPicString(topPIC);
+
+        var writer = new ProFormaWriter();
+
+        Assert.AreEqual(proForma, writer.WriteString(term));
+    }
+
+    /// <summary>
+    /// Testing Exceptions.
+    /// </summary>
+    /// <param name="topPIC">The top pic.</param>
+    [Test]
+    [TestCase("M.A(AAA)[Phospho*4]AAA.C", "multiple mods are not currently supported")]
+    [TestCase("M.A(AAA)[Phospho][Phospho]AAA.C", "multiple mods are not currently supported")]
+    public void ParsingExceptionTesting(string topPIC, string exMessage)
+    {
+        var topicParser = new TopPicProformaParser(GetTestDataFile("topPicTestMods.txt"));
+
+        TestDelegate throwTest = () =>
+        {
+            var term = topicParser.ParseTopPicString(topPIC);
+        };
+
+        TopPicParserException ex = Assert.Throws<TopPicParserException>(throwTest);
+        Assert.AreEqual(exMessage, ex.Message);
+    }
+
+    /// <summary>
+    /// Testing Exceptions.
+    /// </summary>
+    /// <param name="topPIC">The top pic.</param>
+    [Test]
+    [TestCase(@"Phospho,79.966331,STY,any,21,54", "Failed to parse mod file")]
+    [TestCase(@"Phospho,79.966331,STY,any,2O", "Failed to parse UniMod Id 2O")]
+    [TestCase(@"Phospho,79b.966331,STY,any,-1", "invalid UniMod Id or mass")]
+    [TestCase(@"Phospho,79.966331,STY,any,-5", "invalid UniMod Id or mass")]
+    public void ModFilePArsingExceptionTesting(string modFileString, string exMessage)
+    {
+        MemoryStream stream = new MemoryStream(Encoding.UTF8.GetBytes(modFileString));
+
+        TestDelegate throwTest = () =>
+        {     
+            var topicParser = new TopPicProformaParser(stream);
+        };
+
+        TopPicParserException ex = Assert.Throws<TopPicParserException>(throwTest);
+        Assert.AreEqual(exMessage, ex.Message);
+    }
+}
\ No newline at end of file
diff --git a/tests/TopDownProteomics.Tests/TestData/topPicTestMods.txt b/tests/TopDownProteomics.Tests/TestData/topPicTestMods.txt
new file mode 100644
index 0000000..9ad1ed8
--- /dev/null
+++ b/tests/TopDownProteomics.Tests/TestData/topPicTestMods.txt
@@ -0,0 +1,38 @@
+# This file is used to specify modifications
+# # for comments
+# To input a modification, use the following format:
+#
+# Name,Mass,Residues,Position,UnimodID
+#
+# Name: name of the modification (Unimod PSI-MS name)
+# 	- The Unimod PSI-MS names are recommended
+# 	- E.g. Phospho, Acetyl
+# 	- Visit http://www.unimod.org to get PSI-MS names.
+#
+# Mass: monoisotopic mass of modification. 
+#   - It is important to specify accurate masses (integer masses are insufficient).
+# 	- E.g. 15.994915 
+#
+# Residues: amino acids that can be modified
+# 	- Use * if this modification is applicable to all the 20 amino acids. 
+#
+# Position: positions in the protein where the modification can be attached. 
+# 	- Only "any" can be used for anywhere
+#
+# UnimodID: unmimod id of the modification
+#   - Please use -1, if not in unimod
+
+# Methionine oxidation
+Oxidation,15.994915,M,any,35
+
+# Phosphorylation
+Phospho,79.966331,STY,any,21
+
+# test1
+Test1,59.0000,STY,any,-1
+
+# test2
+Test_2,59.0000,STY,any,-1
+
+# test3
+Ox_plus1,17.1230,STY,any,-1
\ No newline at end of file