diff --git a/src/calc/constants.py b/src/calc/constants.py
new file mode 100644
index 0000000..3e45c2f
--- /dev/null
+++ b/src/calc/constants.py
@@ -0,0 +1,57 @@
+"""!
+@file constants.py
+@brief Constants used by the console calculator.
+"""
+
+## Operation symbols, in the order they are offered to the user.
+SYMBOL_ADD: str = "+"
+SYMBOL_SUBTRACT: str = "-"
+SYMBOL_MULTIPLY: str = "*"
+SYMBOL_DIVIDE: str = "/"
+
+## Answers accepted after a calculation.
+ANSWER_CONTINUE: str = "y"
+ANSWER_NEW: str = "n"
+ANSWER_QUIT: str = "q"
+
+## Prompts and messages shown to the user.
+PROMPT_FIRST_NUMBER: str = "What's the first number?: "
+PROMPT_NEXT_NUMBER: str = "What's the next number?: "
+PROMPT_OPERATION: str = "Pick an operation: "
+PROMPT_AGAIN: str = (
+    f"Type '{ANSWER_CONTINUE}' to continue calculating with {{result}}, "
+    f"'{ANSWER_NEW}' to start a new calculation, "
+    f"or '{ANSWER_QUIT}' to quit: "
+)
+MESSAGE_INVALID_NUMBER: str = "That is not a number, please try again."
+MESSAGE_INVALID_OPERATION: str = "That is not a valid operation, please try again."
+MESSAGE_INVALID_ANSWER: str = "Please answer with one of the listed letters."
+MESSAGE_DIVIDE_BY_ZERO: str = "You cannot divide by zero."
+MESSAGE_GOODBYE: str = "Goodbye!"
+
+## ASCII title shown when the program starts.
+ASCII_TITLE: str = r"""
+  ____        _            _       _
+ / ___|__ _  | | ___ _   _| | __ _| |_ ___  _ __
+| |   / _` | | |/ __| | | | |/ _` | __/ _ \| '__|
+| |__| (_| | | | (__| |_| | | (_| | || (_) | |
+ \____\__,_| |_|\___|\__,_|_|\__,_|\__\___/|_|
+"""
+
+## ASCII calculator shown under the title.
+ASCII_CALCULATOR: str = r"""
+ _____________________
+|  _________________  |
+| |               0 | |
+| |_________________| |
+|  ___ ___ ___   ___  |
+| | 7 | 8 | 9 | | + | |
+| |___|___|___| |___| |
+| | 4 | 5 | 6 | | - | |
+| |___|___|___| |___| |
+| | 1 | 2 | 3 | | x | |
+| |___|___|___| |___| |
+| | . | 0 | = | | / | |
+| |___|___|___| |___| |
+|_____________________|
+"""
diff --git a/src/calc/operations.py b/src/calc/operations.py
new file mode 100644
index 0000000..b062846
--- /dev/null
+++ b/src/calc/operations.py
@@ -0,0 +1,63 @@
+"""!
+@file operations.py
+@brief Arithmetic operations and the dictionary that maps symbols to them.
+"""
+
+from collections.abc import Callable
+
+from calc.constants import (
+    SYMBOL_ADD,
+    SYMBOL_DIVIDE,
+    SYMBOL_MULTIPLY,
+    SYMBOL_SUBTRACT,
+)
+
+
+def add(n1: float, n2: float) -> float:
+    """!
+    @brief Add two numbers.
+    @param n1 The first number.
+    @param n2 The second number.
+    @return The sum of @p n1 and @p n2.
+    """
+    return n1 + n2
+
+
+def subtract(n1: float, n2: float) -> float:
+    """!
+    @brief Subtract the second number from the first.
+    @param n1 The first number.
+    @param n2 The second number.
+    @return The difference @p n1 minus @p n2.
+    """
+    return n1 - n2
+
+
+def multiply(n1: float, n2: float) -> float:
+    """!
+    @brief Multiply two numbers.
+    @param n1 The first number.
+    @param n2 The second number.
+    @return The product of @p n1 and @p n2.
+    """
+    return n1 * n2
+
+
+def divide(n1: float, n2: float) -> float:
+    """!
+    @brief Divide the first number by the second.
+    @param n1 The dividend.
+    @param n2 The divisor.
+    @return The quotient @p n1 divided by @p n2.
+    @throws ZeroDivisionError When @p n2 is zero.
+    """
+    return n1 / n2
+
+
+## Maps an operation symbol to its function. The functions are stored, not called.
+OPERATIONS: dict[str, Callable[[float, float], float]] = {
+    SYMBOL_ADD: add,
+    SYMBOL_SUBTRACT: subtract,
+    SYMBOL_MULTIPLY: multiply,
+    SYMBOL_DIVIDE: divide,
+}
diff --git a/tests/test_operations.py b/tests/test_operations.py
new file mode 100644
index 0000000..b4cd59b
--- /dev/null
+++ b/tests/test_operations.py
@@ -0,0 +1,33 @@
+"""!
+@file test_operations.py
+@brief Tests for the arithmetic operations.
+"""
+
+import pytest
+
+from calc.operations import OPERATIONS, add, divide, multiply, subtract
+
+
+def test_add_returns_sum() -> None:
+    assert add(2, 3) == 5
+
+
+def test_subtract_returns_difference() -> None:
+    assert subtract(2, 3) == -1
+
+
+def test_multiply_returns_product() -> None:
+    assert multiply(4, 2.5) == 10
+
+
+def test_divide_returns_quotient() -> None:
+    assert divide(9, 3) == 3
+
+
+def test_divide_when_divisor_is_zero() -> None:
+    with pytest.raises(ZeroDivisionError):
+        divide(1, 0)
+
+
+def test_operations_maps_symbols_to_functions() -> None:
+    assert OPERATIONS == {"+": add, "-": subtract, "*": multiply, "/": divide}