diff --git a/src/main/java/com/mattrixwv/CipherStreamJava/monoSubstitution/Substitution.java b/src/main/java/com/mattrixwv/CipherStreamJava/monoSubstitution/Substitution.java
new file mode 100644
index 0000000..d9c57a0
--- /dev/null
+++ b/src/main/java/com/mattrixwv/CipherStreamJava/monoSubstitution/Substitution.java
@@ -0,0 +1,161 @@
+//CipherStreamJava/src/main/java/com/mattrixwv/CipherStreamJava/monoSubstitution/Substitution.java
+//Mattrixwv
+// Created: 02-22-22
+//Modified: 02-22-22
+package com.mattrixwv.CipherStreamJava.monoSubstitution;
+
+
+import com.mattrixwv.CipherStreamJava.exceptions.InvalidInputException;
+import com.mattrixwv.CipherStreamJava.exceptions.InvalidKeywordException;
+
+
+public class Substitution{
+	private String inputString;
+	private String outputString;
+	private String key;
+	private boolean preserveCapitals;
+	private boolean preserveWhitespace;
+	private boolean preserveSymbols;
+
+	private void setKey(String key) throws InvalidKeywordException{
+		if(key == null){
+			throw new InvalidKeywordException("Key cannot be null");
+		}
+
+		//Transform all letters to uppercase
+		key = key.toUpperCase();
+
+		//Make sure the key contains no duplicate mappings
+		String tempKey = key.replaceAll("(.)\\1{2}", "");
+		if(!tempKey.equals(key)){
+			throw new InvalidKeywordException("The key cannot contain duplicate mappings");
+		}
+
+		//Make sure the key is a valid length
+		if(key.length() == 26){
+			//Make sure the key contains all valid characters
+			tempKey = key.replaceAll("[^A-Z]", "");
+			if(!tempKey.equals(key)){
+				throw new InvalidKeywordException("The key must contain all letters");
+			}
+		}
+		else if(key.length() == 36){
+			//Make sure the key contains all valid characters
+			tempKey = key.replaceAll("[^A-Z0-9]", "");
+			if(!tempKey.equals(key)){
+				throw new InvalidKeywordException("The key must contain all letters and can contain all numbers");
+			}
+		}
+		else{
+			throw new InvalidKeywordException("The key must contain all letters and can contain all numbers");
+		}
+
+		//Save the key
+		this.key = key;
+	}
+	private void setInputString(String inputString) throws InvalidInputException{
+		if(inputString == null){
+			throw new InvalidInputException("Input cannot be null");
+		}
+
+		//Remove any data that should not be preserved
+		if(!preserveCapitals){
+			inputString = inputString.toUpperCase();
+		}
+		if(!preserveWhitespace){
+			inputString = inputString.replaceAll("\\s", "");
+		}
+		if(!preserveSymbols){
+			inputString = inputString.replaceAll("[^a-zA-Z\\s]", "");
+		}
+
+		//Save the inputString
+		this.inputString = inputString;
+
+		//Make sure there is still input
+		if(this.inputString.isBlank()){
+			throw new InvalidInputException("Input must contain at least 1 letter");
+		}
+	}
+	private void encode(){
+		StringBuilder output = new StringBuilder();
+
+		//Step through every character in the inputString and convert it
+		for(char ch : inputString.toCharArray()){
+			if(Character.isUpperCase(ch)){
+				output.append(Character.toUpperCase(key.charAt(ch - 'A')));
+			}
+			else if(Character.isLowerCase(ch)){
+				output.append(Character.toLowerCase(key.charAt(ch - 'a')));
+			}
+			else if(Character.isDigit(ch) && (key.length() == 36)){
+				output.append(key.charAt('Z' - 'A' + Integer.valueOf(Character.toString(ch)) + 1));
+			}
+			else{
+				output.append(ch);
+			}
+		}
+
+		this.outputString = output.toString();
+	}
+	private void decode(){
+		StringBuilder output = new StringBuilder();
+
+		//Step through every character in the inputString and convert it
+		for(char ch : inputString.toCharArray()){
+			if(Character.isUpperCase(ch)){
+				output.append((char)('A' + key.indexOf(Character.toUpperCase(ch))));
+			}
+			else if(Character.isLowerCase(ch)){
+				output.append((char)('a' + key.indexOf(Character.toUpperCase(ch))));
+			}
+			else if(Character.isDigit(ch) && (key.length() == 36)){
+				output.append((char)('0' + (key.indexOf(Character.toUpperCase(ch)) - 26)));
+			}
+			else{
+				output.append(ch);
+			}
+		}
+
+		this.outputString = output.toString();
+	}
+
+	public Substitution(){
+		preserveCapitals = false;
+		preserveWhitespace = false;
+		preserveSymbols = false;
+		reset();
+	}
+	public Substitution(boolean preserveCapitals, boolean preserveWhitespace, boolean preserveSymbols){
+		this.preserveCapitals = preserveCapitals;
+		this.preserveWhitespace = preserveWhitespace;
+		this.preserveSymbols = preserveSymbols;
+		reset();
+	}
+	public String getInputString(){
+		return inputString;
+	}
+	public String getOutputString(){
+		return outputString;
+	}
+	public String getKeyword(){
+		return key;
+	}
+	public String encode(String key, String inputString) throws InvalidKeywordException, InvalidInputException{
+		setKey(key);
+		setInputString(inputString);
+		encode();
+		return outputString;
+	}
+	public String decode(String key, String inputString) throws InvalidKeywordException, InvalidInputException{
+		setKey(key);
+		setInputString(inputString);
+		decode();
+		return outputString;
+	}
+	public void reset(){
+		inputString = "";
+		outputString = "";
+		key = "";
+	}
+}