diff --git a/Conversions/BinaryToDecimal.php b/Conversions/BinaryToDecimal.php
new file mode 100644
index 0000000..b80ab36
--- /dev/null
+++ b/Conversions/BinaryToDecimal.php
@@ -0,0 +1,53 @@
+<?php
+/**
+ * This function converts the
+ * submitted Binary Number to
+ * Decimal Number.
+ *
+ * Working of Algorithm
+ * (10) base 2
+ * (1 * (2 ^ 1) + 0 * (2 ^ 0)) base 10
+ * (2 + 0) base 10
+ * 2 base 10
+ * @param string $binaryNumber
+ * @return int
+ */
+function binaryToDecimal($binaryNumber)
+{
+    if (!is_numeric($binaryNumber)) {
+        throw new \Exception('Please pass a valid Binary Number for Converting it to a Decimal Number.');
+    }
+
+    $decimalNumber = 0;
+    $binaryDigits  = array_reverse(str_split($binaryNumber));
+
+    foreach ($binaryDigits as $index => $digit) {
+        $decimalNumber += $digit * pow(2, $index);
+    }
+
+    return $decimalNumber;
+}
+
+/**
+ * This function converts the
+ * submitted Decimal Number to
+ * Binary Number.
+ *
+ * @param string $decimalNumber
+ * @return string
+ */
+function decimalToBinary($decimalNumber)
+{
+    if (!is_numeric($decimalNumber)) {
+        throw new \Exception('Please pass a valid Decimal Number for Converting it to a Binary Number.');
+    }
+
+    $binaryNumber = '';
+
+    while ($decimalNumber > 0) {
+        $binaryNumber = ($decimalNumber % 2) . $binaryNumber;
+        $decimalNumber /= 2;
+    }
+
+    return $binaryNumber;
+}
diff --git a/Conversions/HexadecimalToDecimal.php b/Conversions/HexadecimalToDecimal.php
new file mode 100644
index 0000000..461506c
--- /dev/null
+++ b/Conversions/HexadecimalToDecimal.php
@@ -0,0 +1,93 @@
+<?php
+/**
+ * This function converts the
+ * submitted Octal Number to
+ * Decimal Number.
+ *
+ * Working of Algorithm
+ * (AB) base 16
+ * (A * (16 ^ 1) + B * (16 ^ 0)) base 10
+ * (10 * (16 ^ 1) + 11 * (16 ^ 0)) base 10
+ * (160 + 11) base 10
+ * 171 base 10
+ * @param string $octalNumber
+ * @return int
+ */
+function hexToDecimal($hexNumber)
+{
+    // Using ctype to check all the digits are valid hex digits or not.
+    if (!ctype_xdigit($hexNumber)) {
+        throw new \Exception('Please pass a valid Hexadecimal Number for Converting it to a Decimal Number.');
+    }
+
+    $decimalNumber = 0;
+
+    // Mapping for Decimal Digits after 9
+    $decimalDigitMappings = [
+        'A' => 10,
+        'B' => 11,
+        'C' => 12,
+        'D' => 13,
+        'E' => 14,
+        'F' => 15,
+    ];
+
+    $hexDigits = str_split($hexNumber);
+    $hexDigits = array_reverse($hexDigits);
+
+    foreach ($hexDigits as $power => $digit) {
+        $hexDigit = $digit;
+        if (!is_numeric($digit)) {
+            $hexDigit = $decimalDigitMappings[$digit];
+        }
+        $decimalNumber += (pow(16, $power) * $hexDigit);
+    }
+    return $decimalNumber;
+}
+
+/**
+ * This function converts the
+ * submitted Decimal Number to
+ * Hexadecimal Number.
+ *
+ * @param string $decimalNumber
+ * @return string
+ */
+function decimalToHex($decimalNumber)
+{
+    $hexDigits = [];
+
+    // Mapping for HexaDecimal Digits after 9
+    $hexDigitMappings = [
+        10 => 'A',
+        11 => 'B',
+        12 => 'C',
+        13 => 'D',
+        14 => 'E',
+        15 => 'F',
+    ];
+    if (!is_numeric($decimalNumber)) {
+        throw new \Exception('Please pass a valid Decimal Number for Converting it to a Hexadecimal Number.');
+    }
+
+    while ($decimalNumber > 0) {
+        $remainder = ($decimalNumber % 16);
+        $decimalNumber /= 16;
+        if (empty($hexDigits) && 0 === $remainder) {
+            continue;
+        }
+        $hexDigits[] = $remainder;
+    }
+
+    $hexDigits = array_reverse($hexDigits);
+
+    foreach ($hexDigits as $index => $digit) {
+        if ($digit > 9) {
+            $hexDigits[$index] = $hexDigitMappings[$digit];
+        }
+    }
+
+    $hexNumber = ltrim(implode('', $hexDigits), '0'); // Connecting all the digits and removing leading zeroes.
+
+    return $hexNumber;
+}
diff --git a/Conversions/OctalToDecimal.php b/Conversions/OctalToDecimal.php
new file mode 100644
index 0000000..cde3638
--- /dev/null
+++ b/Conversions/OctalToDecimal.php
@@ -0,0 +1,53 @@
+<?php
+/**
+ * This function converts the
+ * submitted Octal Number to
+ * Decimal Number.
+ *
+ * Working of Algorithm
+ * (10) base 8
+ * (1 * (8 ^ 1) + 0 * (8 ^ 0)) base 10
+ * (8 + 0) base 10
+ * 9 base 10
+ * @param string $octalNumber
+ * @return int
+ */
+function octalToDecimal($octalNumber)
+{
+    if (!is_numeric($octalNumber)) {
+        throw new \Exception('Please pass a valid Octal Number for Converting it to a Decimal Number.');
+    }
+
+    $decimalNumber = 0;
+    $octalDigits   = array_reverse(str_split($octalNumber));
+
+    foreach ($octalDigits as $index => $digit) {
+        $decimalNumber += $digit * pow(8, $index);
+    }
+
+    return $decimalNumber;
+}
+
+/**
+ * This function converts the
+ * submitted Decimal Number to
+ * Octal Number.
+ *
+ * @param string $decimalNumber
+ * @return string
+ */
+function decimalToOctal($decimalNumber)
+{
+    if (!is_numeric($decimalNumber)) {
+        throw new \Exception('Please pass a valid Decimal Number for Converting it to an Octal Number.');
+    }
+
+    $octalNumber = '';
+
+    while ($decimalNumber > 0) {
+        $octalNumber = ($decimalNumber % 8) . $octalNumber;
+        $decimalNumber /= 8;
+    }
+
+    return $octalNumber;
+}
diff --git a/tests/ConversionsTest.php b/tests/ConversionsTest.php
new file mode 100644
index 0000000..3aa41bc
--- /dev/null
+++ b/tests/ConversionsTest.php
@@ -0,0 +1,71 @@
+<?php
+
+use function PHPUnit\Framework\assertEquals;
+use PHPUnit\Framework\TestCase;
+
+require_once __DIR__ . '/../vendor/autoload.php';
+
+require_once __DIR__ . '/../Conversions/BinaryToDecimal.php';
+require_once __DIR__ . '/../Conversions/OctalToDecimal.php';
+require_once __DIR__ . '/../Conversions/HexadecimalToDecimal.php';
+
+class ConversionsTest extends TestCase
+{
+    public function testBinaryToDecimal()
+    {
+        assertEquals(binaryToDecimal(111), 7);
+        assertEquals(binaryToDecimal(101), 5);
+        $this->expectException(\Exception::class);
+        $this->expectExceptionMessage('Please pass a valid Binary Number for Converting it to a Decimal Number.');
+        binaryToDecimal("this is a string");
+    }
+
+    public function testDecimalToBinary()
+    {
+        assertEquals(decimalToBinary(7), 111);
+        assertEquals(decimalToBinary(5), 101);
+        $this->expectException(\Exception::class);
+        $this->expectExceptionMessage('Please pass a valid Decimal Number for Converting it to a Binary Number.');
+        decimalToBinary("this is a string");
+    }
+
+    public function testOctalToDecimal()
+    {
+        assertEquals(octalToDecimal(10), 8);
+        assertEquals(octalToDecimal(11), 9);
+        assertEquals(octalToDecimal(1115), 589);
+        $this->expectException(\Exception::class);
+        $this->expectExceptionMessage('Please pass a valid Octal Number for Converting it to a Decimal Number.');
+        octalToDecimal("this is a string");
+    }
+
+    public function testDecimalToOctal()
+    {
+        assertEquals(decimalToOctal(8), 10);
+        assertEquals(decimalToOctal(9), 11);
+        assertEquals(decimalToOctal(589), 1115);
+        $this->expectException(\Exception::class);
+        $this->expectExceptionMessage('Please pass a valid Decimal Number for Converting it to an Octal Number.');
+        decimalToOctal("this is a string");
+    }
+
+    public function testDecimalToHex()
+    {
+        assertEquals(decimalToHex(10), 'A');
+        assertEquals(decimalToHex(489201875), '1D28A0D3');
+        assertEquals(decimalToHex(171), 'AB');
+        $this->expectException(\Exception::class);
+        $this->expectExceptionMessage('Please pass a valid Decimal Number for Converting it to a Hexadecimal Number.');
+        decimalToHex("this is a string");
+    }
+
+    public function testHexToDecimal()
+    {
+        assertEquals(hexToDecimal('A'), 10);
+        assertEquals(hexToDecimal('1D28A0D3'), 489201875);
+        assertEquals(hexToDecimal('AB'), 171);
+        $this->expectException(\Exception::class);
+        $this->expectExceptionMessage('Please pass a valid Hexadecimal Number for Converting it to a Decimal Number.');
+        hexToDecimal("this is a string");
+    }
+}